perl - Practical Extraction and Report Language

     perl [options] filename args

     Perl is an interpreted language optimized  for  scanning  arbitrary  text
     files, extracting information from those text files, and printing reports
     based on that information.  It's also a good  language  for  many  system
     management tasks.  The language is intended to be practical (easy to use,
     efficient, complete) rather than beautiful (tiny, elegant, minimal).   It
     combines  (in  the author's opinion, anyway) some of the best features of
     C, sed, awk, and sh, so people familiar with those languages should  have
     little  difficulty  with  it.   (Language  historians will also note some
     vestiges  of  csh,  Pascal,  and  even  BASIC-PLUS.)   Expression  syntax
     corresponds  quite  closely  to  C  expression  syntax.  Unlike most Unix
     utilities, perl does not arbitrarily limit the size  of  your  data----if
     you've  got  the  memory,  perl  can slurp in your whole file as a single
     string.  Recursion is of unlimited depth.  And the hash  tables  used  by
     associative  arrays  grow  as  necessary to prevent degraded performance.
     Perl uses sophisticated pattern matching techniques to scan large amounts
     of  data  very  quickly.   Although optimized for scanning text, perl can
     also deal with binary data, and can make dbm files look like  associative
     arrays  (where  dbm  is available).  Setuid perl scripts are safer than C
     programs through a dataflow tracing mechanism which prevents many  stupid
     security  holes.   If you have a problem that would ordinarily use sed or
     awk or sh, but it exceeds their capabilities or must run a little faster,
     and  you  don't  want to write the silly thing in C, then perl may be for
     you.  There are also translators to turn your sed and  awk  scripts  into
     perl scripts.  OK, enough hype.

     Upon startup, perl looks for your script in one of the following places:

     1.  Specified line by line via -e switches on the command line.

     2.  Contained in the file specified by the first filename on the  command
         line.    (Note   that  systems  supporting  the  #!  notation  invoke
         interpreters this way.)

     3.  Passed in implicitly via standard input.  This only  works  if  there
         are  no filename arguments----to pass arguments to a stdin script you
         must explicitly specify a - for the script name.

     After locating your script, perl compiles it to an internal form.  If the
     script is syntactically correct, it is executed.


     Note: on first reading this section may not make much sense to you.  It's
     here at the front for easy reference.

     A single-character option may be combined with the following  option,  if
     any.   This  is  particularly  useful when invoking a script using the #!
     construct which only allows one argument.  Example:

             #!/usr/bin/perl -spi.bak # same as -s -p -i.bak

     Options include:

          specifies the record separator ($/) as an octal  number.   If  there
          are  no digits, the null character is the separator.  Other switches
          may precede or follow the  digits.   For  example,  if  you  have  a
          version  of  find  which  can print filenames terminated by the null
          character, you can say this:

              find . -name '*.bak' -print0 | perl -n0e unlink

          The special value 00 will cause Perl to  slurp  files  in  paragraph
          mode.   The  value  0777  will cause Perl to slurp files whole since
          there is no legal character with that value.

     -a   turns on autosplit mode when used with a  -n  or  -p.   An  implicit
          split  command to the @F array is done as the first thing inside the
          implicit while loop produced by the -n or -p.

                  perl -ane 'print pop(@F), "\n";'

          is equivalent to

                  while (<>) {
                          @F = split(' ');
                          print pop(@F), "\n";

     -c   causes perl to check the syntax of the script and then exit  without
          executing it.

     -d   runs the script  under  the  perl  debugger.   See  the  section  on

          sets debugging flags.  To watch how it  executes  your  script,  use
          -D14.   (This  only  works if debugging is compiled into your perl.)
          Another nice value is -D1024, which lists your compiled syntax tree.
          And -D512 displays compiled regular expressions.

     -e commandline
          may be used to enter one line of script.  Multiple -e  commands  may
          be given to build up a multi-line script.  If -e is given, perl will
          not look for a script filename in the argument list.

          specifies that files processed by the <> construct are to be  edited
          in-place.   It  does  this  by  renaming the input file, opening the
          output file by the same name, and selecting that output file as  the
          default  for print statements.  The extension, if supplied, is added
          to the name of the old file to make a backup copy.  If no  extension
          is  supplied,  no  backup  is  made.   Saying  ``perl  -p  -i.bak -e
          "s/foo/bar/;" ... '' is the same as using the script:

                  #!/usr/bin/perl -pi.bak

          which is equivalent to

                  while (<>) {
                          if ($ARGV ne $oldargv) {
                                  rename($ARGV, $ARGV . '.bak');
                                  open(ARGVOUT, ">$ARGV");
                                  $oldargv = $ARGV;
                  continue {
                     print; # this prints to original filename

          except that the -i form doesn't need to compare $ARGV to $oldargv to
          know  when  the filename has changed.  It does, however, use ARGVOUT
          for the selected filehandle.  Note that STDOUT is  restored  as  the
          default output filehandle after the loop.

          You can use eof to locate the end of each input file,  in  case  you
          want  to  append  to each file, or reset line numbering (see example
          under eof).

          may be used in conjunction with -P to tell the C preprocessor  where
          to   look   for   include   files.    By  default  /usr/include  and
          /usr/lib/perl are searched.

          enables automatic  line-ending  processing.   It  has  two  effects:
          first,  it automatically chops the line terminator when used with -n
          or -p , and second, it assigns $\ to have the  value  of  octnum  so
          that  any print statements will have that line terminator added back
          on.  If octnum is omitted, sets $\ to the current value of $/.   For
          instance, to trim lines to 80 columns:

                  perl -lpe 'substr($_, 80) = ""'

          Note that the assignment  $\  =  $/  is  done  when  the  switch  is
          processed,  so  the input record separator can be different than the
          output record separator if the -l switch is followed by a -0 switch:

                  gnufind / -print0 | perl -ln0e 'print "found $_" if -p'

          This sets $\ to newline and then sets $/ to the null character.

     -n   causes perl to assume the following loop around your  script,  which
          makes it iterate over filename arguments somewhat like ``sed -n'' or

                  while (<>) {
                          ...             # your script goes here

          Note that the lines are not printed by  default.   See  -p  to  have
          lines  printed.   Here is an efficient way to delete all files older
          than a week:

                  find . -mtime +7 -print | perl -nle 'unlink;'

          This is faster than using the -exec switch of find because you don't
          have to start a process on every filename found.

     -p   causes perl to assume the following loop around your  script,  which
          makes it iterate over filename arguments somewhat like sed:

                  while (<>) {
                          ...             # your script goes here
                  } continue {

          Note that the lines are printed automatically.  To suppress printing
          use the -n switch.  A -p overrides a -n switch.

     -P   causes your script to be  run  through  the  C  preprocessor  before
          compilation  by perl.  (Since both comments and cpp directives begin
          with the # character, you should avoid starting  comments  with  any
          words recognized by the C preprocessor such as ``if'',  ``else''  or

     -s   enables some rudimentary switch parsing for switches on the  command
          line  after  the  script  name but before any filename arguments (or
          before a --).  Any switch found there is removed from @ARGV and sets
          the corresponding variable in the perl script.  The following script
          prints ``true'' if and only if the script is  invoked  with  a  -xyz

                  #!/usr/bin/perl -s
                  if ($xyz) { print "true\n"; }

     -S   makes perl use the PATH  environment  variable  to  search  for  the
          script  (unless  the  name  of  the  script  starts  with  a slash).
          Typically this is used to emulate #! startup on machines that  don't
          support #!, in the following manner:

                  eval "exec /usr/bin/perl -S $0 $*"
                          if $running_under_some_shell;

          The system ignores the first line and feeds the script  to  /bin/sh,
          which  proceeds to try to execute the perl script as a shell script.
          The shell executes the second line as a normal  shell  command,  and
          thus  starts  up  the  perl interpreter.  On some systems $0 doesn't
          always contain the full pathname, so the -S tells perl to search for
          the  script  if necessary.  After perl locates the script, it parses
          the    lines    and    ignores    them    because    the    variable
          $running_under_some_shell is never true.  A better construct than $*
          would be ${1+"$@"}, which handles embedded spaces and  such  in  the
          filenames,  but  doesn't  work if the script is being interpreted by
          csh.  In order to start up sh rather than csh, some systems may have
          to  replace  the  #! line with a line containing just a colon, which
          will be politely ignored by perl.  Other systems can't control that,
          and  need  a  totally  devious construct that will work under any of
          csh, sh or perl, such as the following:

                  eval  '(exit  $?0)'  &&  eval  'exec  /usr/bin/perl  -S   $0
                  & eval 'exec /usr/bin/perl -S $0 $argv:q'
                          if 0;

     -u   causes perl to dump core after compiling your script.  You can  then
          take this core dump and turn it into an executable file by using the
          undump program (not supplied).  This speeds startup at  the  expense
          of  some  disk  space  (which  you  can  minimize  by  stripping the
          executable).  (Still, a "hello world" executable comes out to  about
          200K on my machine.)  If you are going to run your executable  as  a
          set-id  program  then you should probably compile it using taintperl
          rather than normal perl.  If you want to execute a portion  of  your
          script  before  dumping,  use  the  dump  operator  instead.   Note:
          availability of undump is platform specific and may not be available
          for a specific port of perl.

     -U   allows perl to do unsafe operations.  Currently the only  ``unsafe''
          operations  are  the  unlinking  of  directories  while  running  as
          superuser, and running  setuid  programs  with  fatal  taint  checks
          turned into warnings.

     -v   prints the version and patchlevel of your perl executable.

     -w   prints warnings about identifiers that are mentioned only once,  and
          scalar  variables  that are used before being set.  Also warns about
          redefined subroutines, and references to  undefined  filehandles  or
          filehandles  opened  readonly  that  you are attempting to write on.
          Also warns you if you use == on values that don't look like numbers,
          and if your subroutines recurse more than 100 deep.

          tells perl that the  script  is  embedded  in  a  message.   Leading
          garbage  will  be discarded until the first line that starts with #!
          and contains the string "perl".  Any  meaningful  switches  on  that
          line will be applied (but only one group of switches, as with normal
          #! processing).  If a directory name is specified, Perl will  switch
          to  that  directory  before  running the script.  The -x switch only
          controls the the disposal of leading garbage.  The  script  must  be
          terminated  with  __END__ if there is trailing garbage to be ignored
          (the script can process any or all of the trailing garbage  via  the
          DATA filehandle if desired).

     Data Types and Objects

     Perl has three data types: scalars, arrays of  scalars,  and  associative
     arrays  of scalars.  Normal arrays are indexed by number, and associative
     arrays by string.

     The interpretation of operations and values in perl sometimes depends  on
     the requirements of the context around the operation or value.  There are
     three major contexts: string,  numeric  and  array.   Certain  operations
     return  array  values  in  contexts  wanting  an array, and scalar values
     otherwise.  (If this is true of an operation it will be mentioned in  the
     documentation for that operation.)  Operations which return scalars don't
     care whether the context is looking for a string or a number, but  scalar
     variables and values are interpreted as strings or numbers as appropriate
     to the context.  A scalar is interpreted as TRUE in the boolean sense  if
     it is not the null string or 0.  Booleans returned by operators are 1 for
     true and 0 or '' (the null string) for false.
     There are actually two varieties of null string: defined  and  undefined.
     Undefined  null  strings  are  returned  when  there is no real value for
     something, such as when there was an error, or at end of  file,  or  when
     you  refer  to  an  uninitialized  variable  or  element of an array.  An
     undefined null string may become defined the first time  you  access  it,
     but prior to that you can use the defined() operator to determine whether
     the value is defined or not.

     References to scalar variables always begin with `$', even when referring
     to a scalar that is part of an array.  Thus:

         $days               # a simple scalar variable
         $days[28]           # 29th element of array @days
         $days{'Feb'}        # one value from an associative array
         $#days              # last index of array @days

     but entire arrays or array slices are denoted by `@':

         @days               # ($days[0], $days[1],... $days[n])
         @days[3,4,5]        # same as @days[3..5]
         @days{'a','c'}      # same as ($days{'a'},$days{'c'})

     and entire associative arrays are denoted by `%':

         %days               # (key1, val1, key2, val2 ...)

     Any of these eight constructs may serve as an lvalue,  that  is,  may  be
     assigned  to.   (It also turns out that an assignment is itself an lvalue
     in certain contexts----see examples under s, tr and chop.)  Assignment to
     a  scalar  evaluates  the  righthand  side  in  a  scalar  context, while
     assignment to an array or array slice evaluates the righthand side in  an
     array context.

     You may find the length of array @days by evaluating  ``$#days'',  as  in
     csh.   (Actually, it's not the length of the array, it's the subscript of
     the last element, since there is (ordinarily) a 0th element.)   Assigning
     to  $#days  changes the length of the array.  Shortening an array by this
     method does not actually destroy any values.  Lengthening an  array  that
     was previously shortened recovers the values that were in those elements.
     You can also gain some measure of efficiency  by  preextending  an  array
     that  is going to get big.  (You can also extend an array by assigning to
     an element that is off the end of the array.  This differs from assigning
     to  $#whatever  in  that  intervening  values are set to null rather than
     recovered.)  You can truncate an array down to nothing by  assigning  the
     null list () to it.  The following are exactly equivalent

             @whatever = ();
             $#whatever = $[ - 1;

     If you evaluate an array in a scalar context, it returns  the  length  of
     the array.  The following is always true:

             scalar(@whatever) == $#whatever - $[ + 1;

     If you evaluate an associative array in a scalar context,  it  returns  a
     value  which is true if and only if the array contains any elements.  (If
     there are any elements, the value returned is a string consisting of  the
     number  of used buckets and the number of allocated buckets, separated by
     a slash.)

     Multi-dimensional  arrays  are  not  directly  supported,  but  see   the
     discussion  of  the  $;  variable later for a means of emulating multiple
     subscripts with an associative array.  You could also write a  subroutine
     to turn multiple subscripts into a single subscript.

     Every data type  has  its  own  namespace.   You  can,  without  fear  of
     conflict,  use  the  same  name  for  a  scalar  variable,  an  array, an
     associative array, a filehandle,  a  subroutine  name,  and/or  a  label.
     Since  variable  and array references always start with `$', `@', or `%',
     the ``reserved'' words aren't in fact reserved with respect  to  variable
     names.   (They  ARE  reserved  with  respect  to  labels and filehandles,
     however, which don't have an initial special character.  Hint: you  could
     say open(LOG,'logfile') rather than open(log,'logfile').  Using uppercase
     filehandles also improves readability and protects you from conflict with
     future  reserved  words.)   Case  IS  significant----``FOO'', ``Foo'' and
     ``foo'' are all different names.  Names which start  with  a  letter  may
     also  contain  digits  and  underscores.  Names which do not start with a
     letter are limited to one character, e.g. ``$%'' or ``$$''.  (Most of the
     one character names have a predefined significance to perl.  More later.)

     Numeric literals are specified in any of  the  usual  floating  point  or
     integer formats:

         0xffff # hex
         0377 # octal

     String literals are delimited by either single or  double  quotes.   They
     work  much  like shell quotes:  double-quoted string literals are subject
     to backslash and variable substitution;  single-quoted  strings  are  not
     (except  for  \'  and  \\).   The  usual backslash rules apply for making
     characters such as newline, tab, etc., as well as some more exotic forms:

             \t              tab
             \n              newline
             \r              return
             \f              form feed
             \b              backspace
             \a              alarm (bell)
             \e              escape
             \033            octal char
             \x1b            hex char
             \c[             control char
             \l              lowercase next char
             \u              uppercase next char
             \L              lowercase till \E
             \U              uppercase till \E
             \E              end case modification

     You can also embed newlines directly in your strings, i.e. they  can  end
     on  a  different  line  than they begin.  This is nice, but if you forget
     your trailing quote, the error will not  be  reported  until  perl  finds
     another line containing the quote character, which may be much further on
     in the script.  Variable substitution inside strings is limited to scalar
     variables,  normal  array  values,  and  array  slices.  (In other words,
     identifiers beginning with $ or @,  followed  by  an  optional  bracketed
     expression  as a subscript.)  The following code segment prints out ``The
     price is $100.''

         $Price = '$100';                      # not interpreted
         print "The price is $Price.\n";       # interpreted

     Note that you can put curly brackets around the identifier to delimit  it
     from following alphanumerics.  Also note that a single quoted string must
     be separated from a preceding word by a space, since single  quote  is  a
     valid character in an identifier (see Packages).

     Two special literals are  __LINE__  and  __FILE__,  which  represent  the
     current line number and filename at that point in your program.  They may
     only be used as separate tokens;  they  will  not  be  interpolated  into
     strings.   In  addition,  the  token  __END__ may be used to indicate the
     logical end of the script before the actual end of file.   Any  following
     text  is  ignored,  but  may  be read via the DATA filehandle.  (The DATA
     filehandle may read data only from the main  script,  but  not  from  any
     required file or evaluated string.)  The two control characters ^D and ^Z
     are synonyms for __END__.

     A word that doesn't have any other interpretation in the grammar will  be
     treated  as  if it had single quotes around it.  For this purpose, a word
     consists only of alphanumeric characters and underline,  and  must  start
     with  an  alphabetic  character.   As with filehandles and labels, a bare
     word that consists entirely of  lowercase  letters  risks  conflict  with
     future  reserved  words, and if you use the -w switch, Perl will warn you
     about any such words.

     Array values are interpolated into double-quoted strings by  joining  all
     the  elements  of  the  array  with  the  delimiter  specified  in the $"
     variable, space by default.  (Since in versions of perl prior to 3.0  the
     @  character  was  not  a  metacharacter  in  double-quoted  strings, the
     interpolation of @array,  $array[EXPR],  @array[LIST],  $array{EXPR},  or
     @array{LIST} only happens if array is referenced elsewhere in the program
     or is predefined.)  The following are equivalent:

             $temp = join($",@ARGV);
             system "echo $temp";

             system "echo @ARGV";

     Within search patterns (which also undergo  double-quotish  substitution)
     there   is  a  bad  ambiguity:   Is  /$foo[bar]/  to  be  interpreted  as
     /${foo}[bar]/  (where  [bar]  is  a  character  class  for  the   regular
     expression)  or  as  /${foo[bar]}/ (where [bar] is the subscript to array
     @foo)?  If @foo doesn't otherwise exist, then it's obviously a  character
     class.   If  @foo  exists,  perl  takes  a good guess about [bar], and is
     almost always right.  If it does guess wrong, or  if  you're  just  plain
     paranoid, you can force the correct interpretation with curly brackets as

     A line-oriented form of quoting is based on  the  shell  here-is  syntax.
     Following a << you specify a string to terminate the quoted material, and
     all lines following the current line down to the terminating  string  are
     the  value  of  the  item.   The  terminating  string  may  be  either an
     identifier (a word), or some quoted text.  If quoted, the type of  quotes
     you use determines the treatment of the text, just as in regular quoting.
     An unquoted identifier works like double quotes.  There must be no  space
     between  the  <<  and  the  identifier.   (If  you put a space it will be
     treated as a null identifier, which is valid, and matches the first blank
     line----see  Merry Christmas example below.)  The terminating string must
     appear by itself (unquoted and with no  surrounding  whitespace)  on  the
     terminating line.

             print <<EOF;    # same as above
     The price is $Price.

             print <<"EOF";  # same as above
     The price is $Price.

             print << x 10;  # null identifier is delimiter
     Merry Christmas!

             print <<`EOC`;  # execute commands
     echo hi there
     echo lo there

             print <<foo, <<bar; # you can stack them
     I said foo.
     I said bar.

     Array literals are denoted by separating individual values by commas, and
     enclosing the list in parentheses:


     In a context not requiring an array value, the value of the array literal
     is  the  value  of  the  final  element, as in the C comma operator.  For

         @foo = ('cc', '-E', $bar);

     assigns the entire array value to array foo, but

         $foo = ('cc', '-E', $bar);

     assigns the value of variable bar to variable foo.  Note that  the  value
     of  an  actual  array in a scalar context is the length of the array; the
     following assigns to $foo the value 3:

         @foo = ('cc', '-E', $bar);
         $foo = @foo; # $foo gets 3

     You may have an optional comma before the closing parenthesis of an array
     literal, so that you can say:

         @foo = (

     When a LIST is evaluated, each element of the list  is  evaluated  in  an
     array  context,  and  the resulting array value is interpolated into LIST
     just as if each individual element were a member of  LIST.   Thus  arrays
     lose their identity in a LIST----the list


     contains all the elements of @foo followed by all the elements  of  @bar,
     followed by all the elements returned by the subroutine named SomeSub.

     A list value may also be subscripted like a normal array.  Examples:

             $time = (stat($file))[8]; # stat returns array value
             $digit = ('a','b','c','d','e','f')[$digit-10];
             return (pop(@foo),pop(@foo))[0];

     Array lists may be assigned to if and only if each element of the list is
     an lvalue:

         ($a, $b, $c) = (1, 2, 3);

         ($map{'red'}, $map{'blue'}, $map{'green'}) = (0x00f, 0x0f0, 0xf00);

     The final element may be an array or an associative array:

         ($a, $b, @rest) = split;
         local($a, $b, %rest) = @_;

     You can actually put an array anywhere in the list, but the  first  array
     in the list will soak up all the values, and anything after it will get a
     null value.  This may be useful in a local().

     An associative array literal contains pairs of values to  be  interpreted
     as a key and a value:

         # same as map assignment above
         %map = ('red',0x00f,'blue',0x0f0,'green',0xf00);

     Array assignment in a scalar  context  returns  the  number  of  elements
     produced by the expression on the right side of the assignment:

             $x = (($foo,$bar) = (3,2,1)); # set $x to 3, not 2

     There are several other pseudo-literals that you should know about.  If a
     string  is  enclosed  by  backticks  (grave  accents), it first undergoes
     variable substitution just like a  double  quoted  string.   It  is  then
     interpreted  as a command, and the output of that command is the value of
     the pseudo-literal, like in a shell.   In  a  scalar  context,  a  single
     string consisting of all the output is returned.  In an array context, an
     array of values is returned, one for each line of output.  (You  can  set
     $/  to  use  a  different line terminator.)  The command is executed each
     time the pseudo-literal is evaluated.  The status value of the command is
     returned  in  $?  (see  Predefined  Names  for the interpretation of $?).
     Unlike in csh, no translation is  done  on  the  return  data----newlines
     remain  newlines.  Unlike in any of the shells, single quotes do not hide
     variable names in the command from interpretation.  To pass a  $  through
     to the shell you need to hide it with a backslash.

     Evaluating a filehandle in angle brackets yields the next line from  that
     file  (newline  included, so it's never false until EOF, at which time an
     undefined value is returned).  Ordinarily you must assign that value to a
     variable,  but  there  is  one  situation  where  an automatic assignment
     happens.  If (and only if) the input symbol is the only thing inside  the
     conditional  of  a while loop, the value is automatically assigned to the
     variable ``$_''.  (This may seem like an odd thing to you, but you'll use
     the  construct  in  almost  every  perl  script  you write.)  Anyway, the
     following lines are equivalent to each other:

         while ($_ = <STDIN>) { print; }
         while (<STDIN>) { print; }
         for (;<STDIN>;) { print; }
         print while $_ = <STDIN>;
         print while <STDIN>;

     The  filehandles  STDIN,  STDOUT  and  STDERR   are   predefined.    (The
     filehandles  stdin,  stdout and stderr will also work except in packages,
     where they would be interpreted as local identifiers rather than global.)
     Additional filehandles may be created with the open function.

     If a <FILEHANDLE> is used in a context that is looking for an  array,  an
     array  consisting  of all the input lines is returned, one line per array
     element.  It's easy to make a LARGE data space  this  way,  so  use  with

     The null filehandle <> is special and can be used to emulate the behavior
     of  sed and awk.  Input from <> comes either from standard input, or from
     each file listed on the command line.  Here's how  it  works:  the  first
     time  <>  is  evaluated,  the  ARGV  array is checked, and if it is null,
     $ARGV[0] is set to '-', which when opened gives you standard input.   The
     ARGV array is then processed as a list of filenames.  The loop

             while (<>) {
                     ...                     # code for each line

     is equivalent to the following Perl-like pseudo code:

             unshift(@ARGV, '-') if $#ARGV < $[;
             while ($ARGV = shift) {
                     open(ARGV, $ARGV);
                     while (<ARGV>) {
                             ...             # code for each line

     except that it isn't as cumbersome to say, and will  actually  work.   It
     really  does  shift array ARGV and put the current filename into variable
     ARGV.  It also uses filehandle ARGV internally----<> is  just  a  synonym
     for <ARGV>, which is  magical.   (The  pseudo  code  above  doesn't  work
     because it treats <ARGV> as non-magical.)

     You can modify @ARGV before the first <> as long as  the  array  ends  up
     containing  the  list  of  filenames  you really want.  Line numbers ($.)
     continue as if the input was one big happy file.  (But see example  under
     eof for how to reset line numbers on each file.)

     If you want to set @ARGV to your own list of files, go right  ahead.   If
     you  want  to  pass  switches into your script, you can put a loop on the
     front like this:

             while ($_ = $ARGV[0], /^-/) {
                last if /^--$/;
                     /^-D(.*)/ && ($debug = $1);
                     /^-v/ && $verbose++;
                     ...             # other switches
             while (<>) {
                     ...             # code for each line

     The <> symbol will return FALSE only once.  If you call  it  again  after
     this  it  will  assume  you are processing another @ARGV list, and if you
     haven't set @ARGV, will input from STDIN.

     If the string inside the angle  brackets  is  a  reference  to  a  scalar
     variable  (e.g.  <$foo>),  then  that  variable  contains the name of the
     filehandle to input from.

     If  the  string  inside  angle  brackets  is  not  a  filehandle,  it  is
     interpreted  as  a filename pattern to be globbed, and either an array of
     filenames or the next filename in the  list  is  returned,  depending  on
     context.   One level of $ interpretation is done first, but you can't say
     <$foo> because that's an indirect filehandle as explained in the previous
     paragraph.   You could insert curly brackets to force interpretation as a
     filename glob: <${foo}>.  Example:

             while (<*.c>) {
                     chmod 0644, $_;

     is equivalent to

             open(foo, "echo *.c | tr -s ' \t\r\f' '\\012\\012\\012\\012'|");
             while (<foo>) {
                     chmod 0644, $_;

     In fact, it's currently implemented that way.  (Which means it  will  not
     work  on  filenames  with spaces in them unless you have /bin/csh on your
     machine.)  Of course, the shortest way to do the above is:

             chmod 0644, <*.c>;


     A perl script consists of a sequence of declarations and  commands.   The
     only  things  that  need  to  be  declared in perl are report formats and
     subroutines.  See the  sections  below  for  more  information  on  those
     declarations.   All  uninitialized  user-created  objects  are assumed to
     start with a null or 0 value until they  are  defined  by  some  explicit
     operation  such as assignment.  The sequence of commands is executed just
     once, unlike in sed and awk scripts, where the sequence  of  commands  is
     executed  for each input line.  While this means that you must explicitly
     loop over the lines of your input file (or files), it also means you have
     much  more  control  over  which  files  and  which  lines  you  look at.
     (Actually, I'm lying----it is possible to do an implicit loop with either
     the -n or -p switch.)

     A declaration can be put anywhere a command can, but has no effect on the
     execution  of  the  primary sequence of commands----declarations all take
     effect at compile time.  Typically all the declarations are  put  at  the
     beginning or the end of the script.

     Perl is, for the most part, a free-form language.  (The only exception to
     this  is  format declarations, for fairly obvious reasons.)  Comments are
     indicated by the # character, and extend to the end of the line.  If  you
     attempt  to  use  /*  */  C  comments,  it  will be interpreted either as
     division or pattern matching, depending on  the  context.   So  don't  do

     Compound statements

     In perl, a sequence  of  commands  may  be  treated  as  one  command  by
     enclosing it in curly brackets.  We will call this a BLOCK.

     The following compound commands may be used to control flow:

             if (EXPR) BLOCK
             if (EXPR) BLOCK else BLOCK
             if (EXPR) BLOCK elsif (EXPR) BLOCK ... else BLOCK
             LABEL while (EXPR) BLOCK
             LABEL while (EXPR) BLOCK continue BLOCK
             LABEL for (EXPR; EXPR; EXPR) BLOCK
             LABEL foreach VAR (ARRAY) BLOCK
             LABEL BLOCK continue BLOCK

     Note that, unlike C and Pascal, these are defined in terms of BLOCKs, not
     statements.   This  means  that  the  curly  brackets  are required----no
     dangling statements allowed.  If you want to write  conditionals  without
     curly  brackets there are several other ways to do it.  The following all
     do the same thing:

             if (!open(foo)) { die "Can't open $foo: $!"; }
             die "Can't open $foo: $!" unless open(foo);
             open(foo) || die "Can't open $foo: $!"; # foo or bust!
             open(foo) ? 'hi mom' : die "Can't open $foo: $!";
                                     # a bit exotic, that last one

     The if statement is straightforward.  Since BLOCKs are always bounded  by
     curly  brackets, there is never any ambiguity about which if an else goes
     with.  If you use unless in place  of  if,  the  sense  of  the  test  is

     The while statement executes the block as long as the expression is  true
     (does  not evaluate to the null string or 0).  The LABEL is optional, and
     if present, consists of an identifier followed by  a  colon.   The  LABEL
     identifies  the loop for the loop control statements next, last, and redo
     (see below).  If there is a continue BLOCK, it is  always  executed  just
     before  the  conditional is about to be evaluated again, similarly to the
     third part of a for loop in C.  Thus it can be used to increment  a  loop
     variable,  even  when  the loop has been continued via the next statement
     (similar to the C ``continue'' statement).

     If the word while is replaced by the word until, the sense of the test is
     reversed, but the conditional is still tested before the first iteration.

     In either the if or the while statement, you may replace ``(EXPR)''  with
     a  BLOCK, and the conditional is true if the value of the last command in
     that block is true.

     The for loop works exactly like the corresponding while loop:

             for ($i = 1; $i < 10; $i++) {

     is the same as

             $i = 1;
             while ($i < 10) {
             } continue {

     The foreach loop iterates over a normal array value and sets the variable
     VAR  to be each element of the array in turn.  The variable is implicitly
     local to the loop, and regains its former value upon  exiting  the  loop.
     The  ``foreach'' keyword is actually identical to the ``for'' keyword, so
     you can use ``foreach'' for readability or ``for'' for brevity.   If  VAR
     is  omitted,  $_  is  set to each value.  If ARRAY is an actual array (as
     opposed to an expression returning an array value), you can  modify  each
     element of the array by modifying VAR inside the loop.  Examples:

             for (@ary) { s/foo/bar/; }

             foreach $elem (@elements) {
                     $elem *= 2;

             for ((10,9,8,7,6,5,4,3,2,1,'BOOM')) {
                     print $_, "\n"; sleep(1);

             for (1..15) { print "Merry Christmas\n"; }

             foreach $item (split(/:[\\\n:]*/, $ENV{'TERMCAP'})) {
                     print "Item: $item\n";

     The BLOCK by itself (labeled  or  not)  is  equivalent  to  a  loop  that
     executes once.  Thus you can use any of the loop control statements in it
     to leave or restart the block.  The continue  block  is  optional.   This
     construct is particularly nice for doing case structures.

             foo: {
                     if (/^abc/) { $abc = 1; last foo; }
                     if (/^def/) { $def = 1; last foo; }
                     if (/^xyz/) { $xyz = 1; last foo; }
                     $nothing = 1;

     There is no official switch statement in perl, because there are  already
     several  ways  to  write  the  equivalent.  In addition to the above, you
     could write

             foo: {
                     $abc = 1, last foo  if /^abc/;
                     $def = 1, last foo  if /^def/;
                     $xyz = 1, last foo  if /^xyz/;
                     $nothing = 1;

             foo: {
                     /^abc/ && do { $abc = 1; last foo; };
                     /^def/ && do { $def = 1; last foo; };
                     /^xyz/ && do { $xyz = 1; last foo; };
                     $nothing = 1;


             foo: {
                     /^abc/ && ($abc = 1, last foo);
                     /^def/ && ($def = 1, last foo);
                     /^xyz/ && ($xyz = 1, last foo);
                     $nothing = 1;

     or even

             if (/^abc/)
                     { $abc = 1; }
             elsif (/^def/)
                     { $def = 1; }
             elsif (/^xyz/)
                     { $xyz = 1; }
                     {$nothing = 1;}

     As it happens, these are all optimized internally to a switch  structure,
     so  perl  jumps  directly to the desired statement, and you needn't worry
     about perl executing a lot of unnecessary  statements  when  you  have  a
     string  of  50  elsifs, as long as you are testing the same simple scalar
     variable using ==, eq, or pattern matching as above.  (If you're  curious
     as  to  whether  the  optimizer  has  done  this  for  a  particular case
     statement, you can use the -D1024 switch to list the syntax  tree  before

     Simple statements

     The only kind of simple statement is an expression evaluated for its side
     effects.   Every  simple  statement  must be terminated with a semicolon,
     unless it is the final statement in a block, in which case the  semicolon
     is  optional.  (Semicolon is still encouraged there if the block takes up
     more than one line).

     Any simple statement may optionally be followed  by  a  single  modifier,
     just before the terminating semicolon.  The possible modifiers are:

             if EXPR
             unless EXPR
             while EXPR
             until EXPR

     The if and unless modifiers have the expected semantics.  The  while  and
     until  modifiers  also have the expected semantics (conditional evaluated
     first), except when applied to a do-BLOCK or a do-SUBROUTINE command,  in
     which  case  the block executes once before the conditional is evaluated.
     This is so that you can write loops like:

             do {
                     $_ = <STDIN>;
             } until $_ eq ".\n";

     (See the do operator below.  Note also that  the  loop  control  commands
     described  later  will  NOT work in this construct, since modifiers don't
     take loop labels.  Sorry.)


     Since perl expressions work almost exactly like C expressions,  only  the
     differences will be mentioned here.

     Here's what perl has that C doesn't:

     **      The exponentiation operator.

     **=     The exponentiation assignment operator.

     ()      The null list, used to initialize an array to null.

     .       Concatenation of two strings.

     .=      The concatenation assignment operator.

     eq      String equality (== is numeric equality).  For  a  mnemonic  just
             think  of  ``eq''  as  a  string.   (If  you  are used to the awk
             behavior of using == for either string or numeric equality  based
             on  the  current  form  of  the  comparands, beware!  You must be
             explicit here.)

     ne      String inequality (!= is numeric inequality).

     lt      String less than.

     gt      String greater than.

     le      String less than or equal.

     ge      String greater than or equal.

     cmp     String comparison, returning -1, 0, or 1.

     <=>     Numeric comparison, returning -1, 0, or 1.

     =~      Certain operations search or modify the string ``$_'' by default.
             This  operator  makes  that  kind of operation work on some other
             string.  The right argument is a search pattern, substitution, or
             translation.   The  left  argument  is  what  is  supposed  to be
             searched, substituted,  or  translated  instead  of  the  default
             ``$_''.  The return value indicates the success of the operation.
             (If the right argument is  an  expression  other  than  a  search
             pattern,  substitution,  or  translation,  it is interpreted as a
             search pattern at run time.   This  is  less  efficient  than  an
             explicit  search,  since  the pattern must be compiled every time
             the expression is evaluated.)  The precedence of this operator is
             lower  than  unary  minus and autoincrement/decrement, but higher
             than everything else.

     !~      Just like =~ except the return value is negated.

     x       The repetition operator.  Returns a string consisting of the left
             operand  repeated  the  number  of  times  specified by the right
             operand.  In an array context, if the left operand is a  list  in
             parens, it repeats the list.

                     print '-' x 80; # print row of dashes
                     print '-' x80;  # illegal, x80 is identifier

                     print "\t" x ($tab/8), ' ' x ($tab%8); # tab over

                     @ones = (1) x 80; # an array of 80 1's
                     @ones = (5) x @ones; # set all elements to 5

     x=      The repetition assignment operator.  Only works on scalars.

     ..      The range operator,  which  is  really  two  different  operators
             depending  on the context.  In an array context, returns an array
             of values counting (by ones) from the left  value  to  the  right
             value.   This is useful for writing ``for (1..10)'' loops and for
             doing slice operations on arrays.

             In a scalar context, .. returns a boolean value.  The operator is
             bistable,  like  a flip-flop, and emulates the line-range (comma)
             operator of sed, awk, and  various  editors.   Each  ..  operator
             maintains its own boolean state.  It is false as long as its left
             operand is false.  Once the  left  operand  is  true,  the  range
             operator  stays true until the right operand is true, AFTER which
             the range operator becomes false again.  (It doesn't become false
             till  the next time the range operator is evaluated.  It can test
             the right operand and become false  on  the  same  evaluation  it
             became  true (as in awk), but it still returns true once.  If you
             don't want it to test the right operand till the next  evaluation
             (as  in  sed),  use  three dots (...) instead of two.)  The right
             operand is not evaluated while the operator is in  the  ``false''
             state,  and  the left operand is not evaluated while the operator
             is in the ``true'' state.  The precedence is a little lower  than
             ||  and  &&.   The  value  returned is either the null string for
             false, or a sequence number (beginning with  1)  for  true.   The
             sequence  number  is reset for each range encountered.  The final
             sequence number in a range has the string 'E0'  appended  to  it,
             which  doesn't  affect its numeric value, but gives you something
             to search for if you want  to  exclude  the  endpoint.   You  can
             exclude the beginning point by waiting for the sequence number to
             be greater than 1.  If either operand of  scalar  ..  is  static,
             that  operand  is  implicitly  compared  to  the $. variable, the
             current line number.  Examples:

             As a scalar operator:
                 if (101 .. 200) { print; } # print 2nd hundred lines

                 next line if (1 .. /^$/); # skip header lines

                 s/^/> / if (/^$/ .. eof()); # quote body

             As an array operator:
                 for (101 .. 200) { print; } # print $_ 100 times

                 @foo = @foo[$[ .. $#foo]; # an expensive no-op
                 @foo = @foo[$#foo-4 .. $#foo]; # slice last 5 items

     -x      A file test.  This unary operator takes one  argument,  either  a
             filename or a filehandle, and tests the associated file to see if
             something is true about it.  If the argument  is  omitted,  tests
             $_,  except for -t, which tests STDIN.  It returns 1 for true and
             '' for false, or the undefined value if the file  doesn't  exist.
             Precedence  is  higher than logical and relational operators, but
             lower than arithmetic operators.  The operator may be any of:
                     -r      File is readable by effective uid/gid.
                     -w      File is writable by effective uid/gid.
                     -x      File is executable by effective uid/gid.
                     -o      File is owned by effective uid.
                     -R      File is readable by real uid/gid.
                     -W      File is writable by real uid/gid.
                     -X      File is executable by real uid/gid.
                     -O      File is owned by real uid.
                     -e      File exists.
                     -z      File has zero size.
                     -s      File has non-zero size (returns size).
                     -f      File is a plain file.
                     -d      File is a directory.
                     -l      File is a symbolic link.
                     -p      File is a named pipe (FIFO).
                     -S      File is a socket.
                     -b      File is a block special file.
                     -c      File is a character special file.
                     -u      File has setuid bit set.
                     -g      File has setgid bit set.
                     -k      File has sticky bit set.
                     -t      Filehandle is opened to a tty.
                     -T      File is a text file.
                     -B      File is a binary file (opposite of -T).
                     -M      Age of file in days when script started.
                     -A      Same for access time.
                     -C      Same for inode change time.

             The interpretation of the file permission operators -r,  -R,  -w,
             -W,  -x  and  -X  is based solely on the mode of the file and the
             uids and gids of the user.  There may be other reasons you  can't
             actually  read,  write  or execute the file.  Also note that, for
             the superuser, -r, -R, -w and -W always return 1, and -x  and  -X
             return  1  if any execute bit is set in the mode.  Scripts run by
             the superuser may thus need to do a stat() in order to  determine
             the  actual  mode  of  the  file,  or  temporarily set the uid to
             something else.


                     while (<>) {
                             next unless -f $_; # ignore specials

             Note that -s/a/b/ does not do  a  negated  substitution.   Saying
             -exp($foo)   still  works  as  expected,  however----only  single
             letters following a minus are interpreted as file tests.

             The -T and -B switches work as follows.  The first block or so of
             the  file  is examined for odd characters such as strange control
             codes or metacharacters.  If too many odd characters  (>10%)  are
             found,  it's a -B file, otherwise it's a -T file.  Also, any file
             containing null in the first block is considered a  binary  file.
             If -T or -B is used on a filehandle, the current stdio buffer  is
             examined rather than the first block.  Both -T and -B return TRUE
             on a null file, or a file at EOF when testing a filehandle.

     If any of the file tests (or either stat operator) are given the  special
     filehandle consisting of a solitary underline, then the stat structure of
     the previous file test (or stat operator) is used, saving a system  call.
     (This  doesn't  work  with -t, and you need to remember that lstat and -l
     will leave values in the stat structure for the symbolic  link,  not  the
     real file.)  Example:

             print "Can do.\n" if -r $a || -w _ || -x _;

             print "Readable\n" if -r _;
             print "Writable\n" if -w _;
             print "Executable\n" if -x _;
             print "Setuid\n" if -u _;
             print "Setgid\n" if -g _;
             print "Sticky\n" if -k _;
             print "Text\n" if -T _;
             print "Binary\n" if -B _;

     Here is what C has that perl doesn't:

     unary &     Address-of operator.

     unary *     Dereference-address operator.

     (TYPE)      Type casting operator.

     Like C, perl does a certain amount of expression  evaluation  at  compile
     time, whenever it determines that all of the arguments to an operator are
     static and have no side effects.   In  particular,  string  concatenation
     happens   at  compile  time  between  literals  that  don't  do  variable
     substitution.  Backslash interpretation also  happens  at  compile  time.
     You can say

             'Now is the time for all' . "\n" .
             'good men to come to.'

     and this all reduces to one string internally.

     The autoincrement operator has a little extra built-in magic to  it.   If
     you increment a variable that is numeric, or that has ever been used in a
     numeric context, you get a normal increment.  If, however,  the  variable
     has  only  been used in string contexts since it was set, and has a value
     that is  not  null  and  matches  the  pattern  /^[a-zA-Z]*[0-9]*$/,  the
     increment  is  done  as  a  string,  preserving each character within its
     range, with carry:

             print ++($foo = '99'); # prints `100'
             print ++($foo = 'a0'); # prints `a1'
             print ++($foo = 'Az'); # prints `Ba'
             print ++($foo = 'zz'); # prints `aaa'

     The autodecrement is not magical.

     The range operator (in  an  array  context)  makes  use  of  the  magical
     autoincrement  algorithm if the minimum and maximum are strings.  You can

             @alphabet = ('A' .. 'Z');

     to get all the letters of the alphabet, or

             $hexdigit = (0 .. 9, 'a' .. 'f')[$num & 15];

     to get a hexadecimal digit, or

             @z2 = ('01' .. '31');  print @z2[$mday];

     to get dates with leading zeros.  (If the final value specified is not in
     the  sequence that the magical increment would produce, the sequence goes
     until the next value would be longer than the final value specified.)

     The || and && operators differ from C's in that, rather than returning  0
     or  1, they return the last value evaluated. Thus, a portable way to find
     out the home directory might be:

             $home = $ENV{'HOME'} || $ENV{'LOGDIR'} ||
                (getpwuid($<))[7] || die "You're homeless!\n";

     Along with the literals and variables mentioned earlier,  the  operations
     in  the  following  section can serve as terms in an expression.  Some of
     these operations take a LIST as an argument.  Such a list can consist  of
     any  combination  of  scalar  arguments or array values; the array values
     will be  included  in  the  list  as  if  each  individual  element  were
     interpolated  at  that  point  in  the  list,  forming  a  longer single-
     dimensional array value.  Elements of the LIST  should  be  separated  by
     commas.   If  an  operation  is  listed both with and without parentheses
     around its arguments, it means you can either use it as a unary  operator
     or  as  a function call.  To use it as a function call, the next token on
     the same line must be a left  parenthesis.   (There  may  be  intervening
     white  space.)  Such a function then has highest precedence, as you would
     expect from a function.  If any  token  other  than  a  left  parenthesis
     follows, then it is a unary operator, with a precedence depending only on
     whether it is a  LIST  operator  or  not.   LIST  operators  have  lowest
     precedence.  All other unary operators have  a  precedence  greater  than
     relational operators but less than arithmetic operators.  See the section
     on Precedence.

     For operators that can be used in  either  a  scalar  or  array  context,
     failure  is  generally  indicated  in  a  scalar context by returning the
     undefined value, and in an array context  by  returning  the  null  list.
     A SCALAR.  Each operator decides which sort of scalar it  would  be  most
     appropriate to return.  Some operators return the length of the list that
     would have been returned in an array context.  Some operators return  the
     first  value  in  the  list.  Some operators return the last value in the
     list.  Some operators  return  a  count  of  successful  operations.   In
     general, they do what you want, unless you want consistency.

             See m/PATTERN/.

             This is just like the /pattern/ search, except  that  it  matches
             only  once between calls to the reset operator.  This is a useful
             optimization when you only want to see the  first  occurrence  of
             something  in each file of a set of files, for instance.  Only ??
             patterns local to the current package are reset.

             Does the same thing that the accept system  call  does.   Returns
             true if it succeeded, false otherwise.  See example in section on
             Interprocess Communication.


     alarm SECONDS
             Arranges to have a SIGALRM delivered to this  process  after  the
             specified  number  of  seconds  (minus 1, actually) have elapsed.
             Thus, alarm(15) will cause a SIGALRM at some point more  than  14
             seconds  in  the future.  Only one timer may be counting at once.
             Each call disables the previous timer, and an argument of  0  may
             be  supplied  to cancel the previous timer without starting a new
             one.  The returned value is the amount of time remaining  on  the
             previous timer.

             Returns the arctangent of Y/X in the range -PI to PI.

             Does the same thing that the bind system call does.  Returns true
             if  it  succeeded,  false  otherwise.   NAME  should  be a packed
             address of the proper  type  for  the  socket.   See  example  in
             section on Interprocess Communication.


     binmode FILEHANDLE
             Arranges for the file to be read in ``binary'' mode in  operating
             systems  that  distinguish  between binary and text files.  Files
             that are not read in binary mode have CR LF sequences  translated
             to LF on input and LF translated to CR LF on output.  Binmode has
             no effect under Unix.  If FILEHANDLE is an expression, the  value
             is taken as the name of the filehandle.


     caller  Returns the context of the current subroutine call:

                     ($package,$filename,$line) = caller;

             With EXPR, returns some extra information that the debugger  uses
             to  print  a  stack  trace.  The value of EXPR indicates how many
             call frames to go back before the current one.


     chdir EXPR
             Changes the working directory to EXPR, if possible.  If  EXPR  is
             omitted,  changes  to  home directory.  Returns 1 upon success, 0
             otherwise.  See example under die.


     chmod LIST
             Changes the permissions of a list of files.  The first element of
             the list must be the numerical mode.  Returns the number of files
             successfully changed.

                     $cnt = chmod 0755, 'foo', 'bar';
                     chmod 0755, @executables;



     chop VARIABLE

     chop    Chops off  the  last  character  of  a  string  and  returns  the
             character  chopped.   It's  used  primarily to remove the newline
             from the end of an input record, but is much more efficient  than
             s/\n//  because  it  neither  scans  nor  copies  the string.  If
             VARIABLE is omitted, chops $_.  Example:

                     while (<>) {
                             chop;   # avoid \n on last field
                             @array = split(/:/);

             You can actually chop anything that's  an  lvalue,  including  an

                     chop($cwd = `pwd`);
                     chop($answer = <STDIN>);

             If you chop a list, each element is chopped.  Only the  value  of
             the last chop is returned.


     chown LIST
             Changes the owner (and group) of a list of files.  The first  two
             elements  of  the list must be the NUMERICAL uid and gid, in that
             order.  Returns the number of files successfully changed.

                     $cnt = chown $uid, $gid, 'foo', 'bar';
                     chown $uid, $gid, @filenames;

             Here's an example that looks up non-numeric uids  in  the  passwd

                     print "User: ";
                     $user = <STDIN>;
                     print "Files: "
                     $pattern = <STDIN>;
                     open(pass, '/etc/passwd')
                             || die "Can't open passwd: $!\n";
                     while (<pass>) {
                             ($login,$pass,$uid,$gid) = split(/:/);
                             $uid{$login} = $uid;
                             $gid{$login} = $gid;
                     @ary = <${pattern}>; # get filenames
                     if ($uid{$user} eq '') {
                             die "$user not in passwd file";
                     else {
                             chown $uid{$user}, $gid{$user}, @ary;


     chroot FILENAME
             Does the same as the system call of that name.  If you don't know
             what it does, don't worry about it.  If FILENAME is omitted, does
             chroot to $_.


     close FILEHANDLE
             Closes the file or pipe associated with  the  file  handle.   You
             don't have to close FILEHANDLE if you are immediately going to do
             another open on it, since open  will  close  it  for  you.   (See
             open.)   However,  an  explicit close on an input file resets the
             line counter ($.), while the implicit close  done  by  open  does
             not.  Also, closing a pipe will wait for the process executing on
             the pipe to complete, in case you want to look at the  output  of
             the  pipe  afterwards.   Closing  a pipe explicitly also puts the
             status value of the command into $?.  Example:

                     open(OUTPUT, '|sort >foo'); # pipe to sort
                     ...     # print stuff to output
                     close OUTPUT;   # wait for sort to finish
                     open(INPUT, 'foo'); # get sort's results

             FILEHANDLE may be  an  expression  whose  value  gives  the  real
             filehandle name.


     closedir DIRHANDLE
             Closes a directory opened by opendir().

             Does the same thing that the connect system call  does.   Returns
             true  if it succeeded, false otherwise.  NAME should be a package
             address of the proper  type  for  the  socket.   See  example  in
             section on Interprocess Communication.


     cos EXPR
             Returns the cosine of EXPR (expressed in radians).   If  EXPR  is
             omitted takes cosine of $_.

             Encrypts a string exactly like the  crypt()  function  in  the  C
             library.   Useful  for  checking  the  password  file  for  lousy
             passwords.  Only the guys wearing white hats should do this.


     dbmclose ASSOC_ARRAY
             Breaks the binding between a dbm file and an  associative  array.
             The  values  remaining  in  the associative array are meaningless
             unless you happen to want to know what was in the cache  for  the
             dbm file.  This function is only useful if you have ndbm.

             This binds a dbm or ndbm file to an associative array.  ASSOC  is
             the  name  of  the  associative  array.  (Unlike normal open, the
             first argument is NOT a filehandle, even  though  it  looks  like
             one).   DBNAME  is  the name of the database (without the .dir or
             .pag extension).  If the database does not exist, it  is  created
             with protection specified by MODE (as modified by the umask).  If
             your system only  supports  the  older  dbm  functions,  you  may
             perform  only  one  dbmopen  in your program.  If your system has
             neither dbm nor ndbm, calling dbmopen produces a fatal error.

             Values assigned to the associative array prior to the dbmopen are
             lost.  A certain number of values from the dbm file are cached in
             memory.  By default this number is 64, but you can increase it by
             preallocating  that  number of garbage entries in the associative
             array before the dbmopen.  You can flush the cache  if  necessary
             with the reset command.

             If you don't have write access to the dbm file, you can only read
             associative  array  variables, not set them.  If you want to test
             whether you can write, either use file tests  or  try  setting  a
             dummy array entry inside an eval, which will trap the error.

             Note that functions such as keys() and values() may  return  huge
             array values when used on large dbm files.  You may prefer to use
             the each() function to iterate over large dbm files.  Example:

                     # print out history file offsets
                     while (($key,$val) = each %HIST) {
                             print $key, ' = ', unpack('L',$val), "\n";


     defined EXPR
             Returns a boolean value saying whether the lvalue EXPR has a real
             value  or  not.  Many operations return the undefined value under
             exceptional  conditions,  such  as  end  of  file,  uninitialized
             variable,  system  error  and  such.  This function allows you to
             distinguish between an undefined null string and a  defined  null
             string  with  operations that might return a real null string, in
             particular referencing elements of an array.  You may also  check
             to  see  if  arrays  or  subroutines  exist.   Use  on predefined
             variables  is  not  guaranteed  to  produce  intuitive   results.

                     print if defined $switch{'D'};
                     print "$val\n" while defined($val = pop(@ary));
                     die "Can't readlink $sym: $!"
                             unless defined($value = readlink $sym);
                     eval '@foo = ()' if defined(@foo);
                     die "No XYZ package defined" unless defined %_XYZ;
                     sub foo { defined &$bar ? &$bar(@_) : die "No bar"; }

             See also undef.

     delete $ASSOC{KEY}
             Deletes the specified value from the specified associative array.
             Returns  the deleted value, or the undefined value if nothing was
             deleted.   Deleting  from  $ENV{}   modifies   the   environment.
             Deleting from an array bound to a dbm file deletes the entry from
             the dbm file.

             The following deletes all the values of an associative array:

                     foreach $key (keys %ARRAY) {
                             delete $ARRAY{$key};

             (But it would be faster to use the reset command.   Saying  undef
             %ARRAY is faster yet.)


     die LIST
             Outside of an eval, prints the value of LIST to STDERR and  exits
             with  the  current  value of $!  (errno).  If $! is 0, exits with
             the value of ($? >> 8) (`command` status).  If ($? >>  8)  is  0,
             exits  with  255.   Inside  an eval, the error message is stuffed
             into $@ and the eval is terminated with the undefined value.

             Equivalent examples:

                     die "Can't cd to spool: $!\n"
                             unless chdir '/usr/spool/news';

                     chdir '/usr/spool/news' || die "Can't cd to spool: $!\n"

             If the value of EXPR does not  end  in  a  newline,  the  current
             script  line  number  and  input  line  number  (if any) are also
             printed, and a newline is supplied.   Hint:  sometimes  appending
             ``,  stopped'' to your message will cause it to make better sense
             when the string ``at foo line 123'' is appended.  Suppose you are
             running script ``canasta''.

                     die "/etc/games is no good";
                     die "/etc/games is no good, stopped";

             produce, respectively

                     /etc/games is no good at canasta line 123.
                     /etc/games is no good, stopped at canasta line 123.

             See also exit.

     do BLOCK
             Returns the value of the last command in the sequence of commands
             indicated  by  BLOCK.  When modified by a loop modifier, executes
             the BLOCK once before testing  the  loop  condition.   (On  other
             statements the loop modifiers test the conditional first.)

             Executes a SUBROUTINE declared by a sub declaration, and  returns
             the  value  of  the  last expression evaluated in SUBROUTINE.  If
             there is no subroutine by that  name,  produces  a  fatal  error.
             (You   may  use  the  ``defined''  operator  to  determine  if  a
             subroutine exists.)  If you pass arrays as part of LIST  you  may
             wish  to  pass  the  length  of the array in front of each array.
             (See the section on subroutines later on.)  The  parentheses  are
             required to avoid confusion with the ``do EXPR'' form.

             SUBROUTINE may also be a single scalar variable,  in  which  case
             the name of the subroutine to execute is taken from the variable.

             As an alternate (and preferred) form, you may call  a  subroutine
             by  prefixing  the  name  with an ampersand: &foo(@args).  If you
             aren't passing any arguments, you don't have to use  parentheses.
             If  you  omit  the  parentheses,  no  @_  array  is passed to the
             subroutine.  The & form is also used to  specify  subroutines  to
             the defined and undef operators:

                     if (defined &$var) { &$var($parm); undef &$var; }

     do EXPR Uses the value of EXPR as a filename and executes the contents of
             the  file  as  a  perl  script.   Its  primary  use is to include
             subroutines from a perl subroutine library.

                     do '';

             is just like

                     eval `cat`;

             except that it's more efficient, more concise, keeps track of the
             current  filename  for  error  messages,  and searches all the -I
             libraries if the file isn't in the current  directory  (see  also
             the  @INC array in Predefined Names).  It's the same, however, in
             that it does reparse the file every time you call it, so  if  you
             are  going  to use the file inside a loop you might prefer to use
             -P and #include, at the expense of a little  more  startup  time.
             (The  main  problem  with  #include  is  that  cpp doesn't grok #
             comments----a  workaround  is  to  use  ``;#''   for   standalone
             comments.)  Note that the following are NOT equivalent:

                     do $foo; # eval a file
                     do $foo(); # call a subroutine

             Note that inclusion of library routines is better done  with  the
             ``require'' operator.

     dump LABEL
             This causes an immediate core dump.  Primarily this  is  so  that
             you  can  use  the  undump program to turn your core dump into an
             executable binary after having initialized all your variables  at
             the beginning of the program.  When the new binary is executed it
             will begin by executing a "goto LABEL" (with all the restrictions
             that  goto  suffers).   Think of it as a goto with an intervening
             core dump and reincarnation.  If LABEL is omitted,  restarts  the
             program  from  the top.  WARNING: any files opened at the time of
             the  dump  will  NOT  be  open  any  more  when  the  program  is
             reincarnated,  with  possible  resulting confusion on the part of
             perl.  See also -u.


                     require '';
                     require '';
                     %days = (

                     dump QUICKSTART if $ARGV[0] eq '-d';

                     do Getopt('f');


     each ASSOC_ARRAY
             Returns a 2 element array consisting of the key and value for the
             next  value of an associative array, so that you can iterate over
             it.  Entries are returned in an apparently  random  order.   When
             the  array is entirely read, a null array is returned (which when
             assigned produces a FALSE (0) value).  The next  call  to  each()
             after that will start iterating again.  The iterator can be reset
             only by reading all the elements from the array.   You  must  not
             modify  the  array  while  iterating  over it.  There is a single
             iterator for each associative array, shared by all each(), keys()
             and values() function calls in the program.  The following prints
             out your  environment  like  the  printenv  program,  only  in  a
             different order:

                     while (($key,$value) = each %ENV) {
                             print "$key=$value\n";

             See also keys() and values().



     eof     Returns 1 if the next read on FILEHANDLE will return end of file,
             or  if  FILEHANDLE  is not open.  FILEHANDLE may be an expression
             whose value gives the real  filehandle  name.   (Note  that  this
             function  actually  reads a character and then ungetc's it, so it
             is not very useful in an interactive context.)  An eof without an
             argument  returns  the  eof status for the last file read.  Empty
             parentheses () may be used to indicate the pseudo file formed  of
             the files listed on the command line, i.e. eof() is reasonable to
             use inside a while (<>) loop to detect the end of only  the  last
             file.   Use eof(ARGV) or eof without the parentheses to test EACH
             file in a while (<>) loop.  Examples:

                     # insert dashes just before last line of last file
                     while (<>) {
                             if (eof()) {
                                     print "--------------\n";

                     # reset line numbering on each input file
                     while (<>) {
                             print "$.\t$_";
                             if (eof) { # Not eof().


     eval EXPR

     eval BLOCK
             EXPR is parsed and executed as if it were a little perl  program.
             It  is  executed  in  the context of the current perl program, so
             that any variable  settings,  subroutine  or  format  definitions
             remain  afterwards.   The value returned is the value of the last
             expression evaluated, just as with subroutines.  If  there  is  a
             syntax error or runtime error, or a die statement is executed, an
             undefined value is returned by eval, and $@ is set to  the  error
             message.   If  there  was no error, $@ is guaranteed to be a null
             string.  If EXPR is omitted, evaluates $_.  The final  semicolon,
             if any, may be omitted from the expression.

             Note that, since eval traps otherwise-fatal errors, it is  useful
             for  determining whether a particular feature (such as dbmopen or
             symlink) is implemented.  It is also  Perl's  exception  trapping
             mechanism, where the die operator is used to raise exceptions.

             If the code to be executed doesn't vary, you may  use  the  eval-
             BLOCK  form to trap run-time errors without incurring the penalty
             of recompiling each time.  The error, if any, is  still  returned
             in  $@.  Evaluating a single-quoted string (as EXPR) has the same
             effect, except that the eval-EXPR form reports syntax  errors  at
             run  time  via  $@,  whereas  the  eval-BLOCK form reports syntax
             errors at compile time.  The eval-EXPR form is optimized to eval-
             BLOCK the first time it succeeds.  (Since the replacement side of
             a substitution is considered a single-quoted string when you  use
             the e modifier, the same optimization occurs there.)  Examples:

                     # make divide-by-zero non-fatal
                     eval { $answer = $a / $b; }; warn $@ if $@;

                     # optimized to same thing after first use
                     eval '$answer = $a / $b'; warn $@ if $@;

                     # a compile-time error
                     eval { $answer = };

                     # a run-time error
                     eval '$answer ='; # sets $@


     exec LIST
             If there is more than one argument in LIST,  or  if  LIST  is  an
             array with more than one value, calls execvp() with the arguments
             in LIST.  If there is only one scalar argument, the  argument  is
             checked  for  shell metacharacters.  If there are any, the entire
             argument is passed to ``/bin/sh -c'' for parsing.  If  there  are
             none,  the  argument  is  split into words and passed directly to
             execvp(), which is more efficient.  Note: exec  (and  system)  do
             not  flush your output buffer, so you may need to set $| to avoid
             lost output.  Examples:

                     exec '/bin/echo', 'Your arguments are: ', @ARGV;
                     exec "sort $outfile | uniq";

             If you don't really want to execute the first argument, but  want
             to  lie  to the program you are executing about its own name, you
             can specify the program you actually want  to  run  by  assigning
             that  to a variable and putting the name of the variable in front
             of the LIST without a comma.  (This always forces  interpretation
             of  the  LIST  as  a  multi-valued  list, even if there is only a
             single scalar in the list.)  Example:

                     $shell = '/bin/csh';
                     exec $shell '-sh'; # pretend it's a login shell


     exit EXPR
             Evaluates EXPR and exits immediately with that value.  Example:

                     $ans = <STDIN>;
                     exit 0 if $ans =~ /^[Xx]/;

             See also die.  If EXPR is omitted, exits with 0 status.


     exp EXPR
             Returns e to the power  of  EXPR.   If  EXPR  is  omitted,  gives

             Implements the fcntl(2) function.  You'll probably have to say

                     require          "";          #          probably

             first to get  the  correct  function  definitions.   If
             doesn't exist or doesn't have the correct definitions you'll have
             to  roll  your  own,  based  on  your  C  header  files  such  as
             <sys/fcntl.h>.   (There  is  a perl script called h2ph that comes
             with the  perl  kit  which  may  help  you  in  this.)   Argument
             processing  and  value  return works just like ioctl below.  Note
             that fcntl will produce a fatal error if used on a  machine  that
             doesn't implement fcntl(2).


     fileno FILEHANDLE
             Returns  the  file  descriptor  for  a  filehandle.   Useful  for
             constructing   bitmaps   for   select().   If  FILEHANDLE  is  an
             expression, the value is taken as the name of the filehandle.

             Calls flock(2) on FILEHANDLE.  See manual page for  flock(2)  for
             definition  of  OPERATION.   Returns  true  for success, false on
             failure.  Will produce a fatal error if used on  a  machine  that
             doesn't  implement  flock(2).   Here's a mailbox appender for BSD

                     $LOCK_SH = 1;
                     $LOCK_EX = 2;
                     $LOCK_NB = 4;
                     $LOCK_UN = 8;

                     sub lock {
                        # and, in case someone appended
                        # while we were waiting...
                        seek(MBOX, 0, 2);

                     sub unlock {

                     open(MBOX, ">>/usr/spool/mail/$ENV{'USER'}")
                             || die "Can't open mailbox: $!";

                     do lock();
                     print MBOX $msg,"\n\n";
                     do unlock();

     fork    Does a fork() call.  Returns the child pid to the parent  process
             and  0  to  the  child  process.   Note: unflushed buffers remain
             unflushed in both processes, which means you may need to  set  $|
             to avoid duplicate output.


     getc FILEHANDLE

     getc    Returns the next  character  from  the  input  file  attached  to
             FILEHANDLE,  or  a null string at EOF.  If FILEHANDLE is omitted,
             reads from STDIN.

             Returns the current login from /etc/utmp, if any.  If  null,  use

                     $login = getlogin || (getpwuid($<))[0] || "Somebody";

             Returns the packed sockaddr address of other end  of  the  SOCKET

                     # An internet sockaddr
                     $sockaddr = 'S n a4 x8';
                     $hersockaddr = getpeername(S);
                     ($family, $port, $heraddr) =


     getpgrp PID
             Returns the current process group for the specified  PID,  0  for
             the  current  process.   Will  produce a fatal error if used on a
             machine that doesn't implement getpgrp(2).  If EXPR  is  omitted,
             returns process group of current process.

     getppid Returns the process id of the parent process.

             Returns the current priority for a process, a process group, or a
             user.   (See getpriority(2).)  Will produce a fatal error if used
             on a machine that doesn't implement getpriority(2).






























             These routines perform the same functions as  their  counterparts
             in  the  system  library.   Within  an  array context, the return
             values from the various get routines are as follows:

                       $quota,$comment,$gcos,$dir,$shell) = getpw...
                     ($name,$passwd,$gid,$members) = getgr...
                     ($name,$aliases,$addrtype,$length,@addrs) = gethost...
                     ($name,$aliases,$addrtype,$net) = getnet...
                     ($name,$aliases,$proto) = getproto...
                     ($name,$aliases,$port,$proto) = getserv...

             (If the entry doesn't exist you get a null list.)

             Within a scalar context, you get the name,  unless  the  function
             was  a  lookup  by  name,  in which case you get the other thing,
             whatever it  is.   (If  the  entry  doesn't  exist  you  get  the
             undefined value.)  For example:

                     $uid = getpwnam
                     $name = getpwuid
                     $name = getpwent
                     $gid = getgrnam
                     $name = getgrgid
                     $name = getgrent

             The $members value returned by getgr... is a space separated list
             of the login names of the members of the group.

             For  the  gethost...  functions,  if  the  h_errno  variable   is
             supported in C, it will be returned to you via $? if the function
             call fails.  The @addrs value returned by a successful call is  a
             list  of  the  raw addresses returned by the corresponding system
             library call.  In the Internet domain, each address is four bytes
             long and you can unpack it by saying something like:

                     ($a,$b,$c,$d) = unpack('C4',$addr[0]);

             Returns the packed sockaddr address of this  end  of  the  SOCKET

                     # An internet sockaddr
                     $sockaddr = 'S n a4 x8';
                     $mysockaddr = getsockname(S);
                     ($family, $port, $myaddr) =

             Returns the socket option requested, or undefined if there is  an


     gmtime EXPR
             Converts a time as returned by the time function to  a  9-element
             array   with  the  time  analyzed  for  the  Greenwich  timezone.
             Typically used as follows:

                 ($sec,$min,$hour,$mday,$mon,$year,$wday,$yday,$isdst) =

             All array elements are numeric, and come straight out of a struct
             tm.   In  particular this means that $mon has the range 0..11 and
             $wday has the range 0..6.  If EXPR is omitted, does gmtime(time).

     goto LABEL
             Finds the statement labeled  with  LABEL  and  resumes  execution
             there.   Currently you may only go to statements in the main body
             of the program that are not nested  inside  a  do  {}  construct.
             This  statement  is not implemented very efficiently, and is here
             only to make the sed-to-perl translator easier.  I may change its
             semantics at any time, consistent with support for translated sed
             scripts.  Use it at your own risk.  Better yet, don't use  it  at

             Evaluates EXPR for each element of LIST (locally  setting  $_  to
             each  element)  and  returns  the array value consisting of those
             elements for which the expression evaluated to true.  In a scalar
             context, returns the number of times the expression was true.

                     @foo = grep(!/^#/, @bar);    # weed out comments

             Note that, since $_ is a reference into the array value,  it  can
             be  used  to  modify  the  elements  of the array.  While this is
             useful and supported, it can cause bizarre results if the LIST is
             not a named array.


     hex EXPR
             Returns the decimal value of EXPR interpreted as an  hex  string.
             (To  interpret  strings that might start with 0 or 0x see oct().)
             If EXPR is omitted, uses $_.


             Returns the position of the first occurrence of SUBSTR in STR  at
             or after POSITION.  If POSITION is omitted, starts searching from
             the beginning of the string.  The return value is based at 0,  or
             whatever  you've set the $[ variable to.  If the substring is not
             found, returns one less than the base, ordinarily -1.


     int EXPR
             Returns the integer portion of EXPR.  If EXPR  is  omitted,  uses

             Implements the ioctl(2) function.  You'll probably have to say

                     require          "";          #          probably

             first to get  the  correct  function  definitions.   If
             doesn't exist or doesn't have the correct definitions you'll have
             to  roll  your  own,  based  on  your  C  header  files  such  as
             <sys/ioctl.h>.   (There  is  a perl script called h2ph that comes
             with the perl kit which may help you in this.)   SCALAR  will  be
             read and/or written depending on the FUNCTION----a pointer to the
             string value of SCALAR will be passed as the  third  argument  of
             the  actual  ioctl call.  (If SCALAR has no string value but does
             have a numeric value, that value will be  passed  rather  than  a
             pointer to the string value.  To guarantee this to be true, add a
             0 to the scalar  before  using  it.)   The  pack()  and  unpack()
             functions  are  useful  for manipulating the values of structures
             used by ioctl().  The following example sets the erase  character
             to DEL.

                     require '';
                     $sgttyb_t = "ccccs"; # 4 chars and a short
                     if (ioctl(STDIN,$TIOCGETP,$sgttyb)) {
                             @ary = unpack($sgttyb_t,$sgttyb);
                             $ary[2] = 127;
                             $sgttyb = pack($sgttyb_t,@ary);
                                     || die "Can't ioctl: $!";

             The return value of ioctl (and fcntl) is as follows:

                      if OS returns:             perl returns:
                       -1                         undefined value
                       0                          string "0 but true"
                       anything else              that number

             Thus perl returns true on success and false on failure,  yet  you
             can  still  easily  determine  the  actual  value returned by the
             operating system:

                     ($retval = ioctl(...)) || ($retval = -1);
                     printf "System returned %d\n", $retval;


             Joins the separate strings of LIST or ARRAY into a single  string
             with  fields  separated  by  the  value  of EXPR, and returns the
             string.  Example:

                 $_ = join(':',

             See split.


     keys ASSOC_ARRAY
             Returns a normal array consisting of all the keys  of  the  named
             associative array.  The keys are returned in an apparently random
             order, but it is the same order as either the values() or  each()
             function  produces (given that the associative array has not been
             modified).  Here is yet another way to print your environment:

                     @keys = keys %ENV;
                     @values = values %ENV;
                     while ($#keys >= 0) {
                             print pop(@keys), '=', pop(@values), "\n";

             or how about sorted by key:

                     foreach $key (sort(keys %ENV)) {
                             print $key, '=', $ENV{$key}, "\n";


     kill LIST
             Sends a signal to a list of processes.  The first element of  the
             list must be the signal to send.  Returns the number of processes
             successfully signaled.

                     $cnt = kill 1, $child1, $child2;
                     kill 9, @goners;

             If the signal  is  negative,  kills  process  groups  instead  of
             processes.   (On  System  V,  a negative process number will also
             kill process groups, but that's not portable.)   You  may  use  a
             signal name in quotes.

     last LABEL

     last    The last command is like the break statement in  C  (as  used  in
             loops);  it immediately exits the loop in question.  If the LABEL
             is omitted, the command refers to the innermost  enclosing  loop.
             The continue block, if any, is not executed:

                     line: while (<STDIN>) {
                             last line if /^$/; # exit when done with header


     length EXPR
             Returns the length in characters of the value of EXPR.   If  EXPR
             is omitted, returns length of $_.

             Creates a new filename linked to the old filename.  Returns 1 for
             success, 0 otherwise.

             Does the same thing that the listen system  call  does.   Returns
             true if it succeeded, false otherwise.  See example in section on
             Interprocess Communication.

             Declares the listed variables to be local to the enclosing block,
             subroutine,  eval  or  ``do''.   All  the listed elements must be
             legal lvalues.  This operator works by saving the current  values
             of  those  variables in LIST on a hidden stack and restoring them
             upon exiting the block, subroutine  or  eval.   This  means  that
             called subroutines can also reference the local variable, but not
             the global one.  The LIST may be assigned to  if  desired,  which
             allows   you   to   initialize  your  local  variables.   (If  no
             initializer is given for a particular  variable,  it  is  created
             with  an  undefined  value.)   Commonly  this is used to name the
             parameters to a subroutine.  Examples:

                     sub RANGEVAL {
                             local($min, $max, $thunk) = @_;
                             local($result) = '';

                             # Presumably $thunk makes reference to $i

                             for ($i = $min; $i < $max; $i++) {
                                     $result .= eval $thunk;


                     if ($sw eq '-v') {
                        # init local array with global array
                        local(@ARGV) = @ARGV;
                        system @ARGV;
                     # @ARGV restored

                     # temporarily add to digits associative array
                     if ($base12) {
                             # (NOTE: not claiming this is efficient!)
                             local(%digits) = (%digits,'t',10,'e',11);
                             do parse_num();

             Note that local() is a run-time command,  and  so  gets  executed
             every  time through a loop, using up more stack storage each time
             until it's all released at once when the loop is exited.


     localtime EXPR
             Converts a time as returned by the time function to  a  9-element
             array  with  the time analyzed for the local timezone.  Typically
             used as follows:

                 ($sec,$min,$hour,$mday,$mon,$year,$wday,$yday,$isdst) =

             All array elements are numeric, and come straight out of a struct
             tm.   In  particular this means that $mon has the range 0..11 and
             $wday  has  the  range  0..6.    If   EXPR   is   omitted,   does


     log EXPR
             Returns logarithm (base e) of EXPR.  If EXPR is omitted,  returns
             log of $_.


     lstat FILEHANDLE


             Does the same thing as the stat() function, but stats a  symbolic
             link  instead  of  the  file  the  symbolic  link  points to.  If
             symbolic links are unimplemented on your system, a normal stat is


             Searches a string for a pattern match, and returns  true  (1)  or
             false ('').  If no string is specified via the =~ or !~ operator,
             the $_ string is searched.  (The string specified  with  =~  need
             not  be  an  lvalue----it  may  be  the  result  of an expression
             evaluation, but remember the =~ binds rather tightly.)  See  also
             the section on regular expressions.

             If / is the delimiter then the initial `m' is optional.  With the
             `m'  you  can  use  any  pair  of  non-alphanumeric characters as
             delimiters.  This is particularly useful for matching  Unix  path
             names  that  contain  `/'.  If the final delimiter is followed by
             the optional  letter  `i',  the  matching  is  done  in  a  case-
             insensitive  manner.   PATTERN  may  contain references to scalar
             variables,  which  will  be   interpolated   (and   the   pattern
             recompiled)  every  time  the pattern search is evaluated.  (Note
             that $) and $| may not be interpolated  because  they  look  like
             end-of-string  tests.)  If you want such a pattern to be compiled
             only once, add an  ``o''  after  the  trailing  delimiter.   This
             avoids  expensive run-time recompilations, and is useful when the
             value you are interpolating won't change over  the  life  of  the
             script.   If  the  PATTERN  evaluates  to a null string, the most
             recent successful regular expression is used instead.

             If used in a context that requires  an  array  value,  a  pattern
             match  returns  an array consisting of the subexpressions matched
             by the parentheses in the pattern, i.e. ($1, $2, $3...).  It does
             NOT  actually  set $1, $2, etc. in this case, nor does it set $+,
             $`, $& or $'.  If the match fails, a null array is returned.   If
             the match succeeds, but there were no parentheses, an array value
             of (1) is returned.


                 open(tty, '/dev/tty');
                 <tty> =~ /^y/i && do foo(); # do foo if desired

                 if (/Version: *([0-9.]*)/) { $version = $1; }

                 next if m#^/usr/spool/uucp#;

                 # poor man's grep
                 $arg = shift;
                 while (<>) {
                        print if /$arg/o; # compile only once

                 if (($F1, $F2, $Etc) = ($foo =~ /^(\S+)\s+(\S+)\s*(.*)/))

             This last example splits $foo into the first two  words  and  the
             remainder of the line, and assigns those three fields to $F1, $F2
             and  $Etc.   The  conditional  is  true  if  any  variables  were
             assigned, i.e. if the pattern matched.

             The ``g'' modifier specifies global pattern matching----that  is,
             matching  as  many  times  as possible within the string.  How it
             behaves depends on the context.  In an array context, it  returns
             a  list  of  all the substrings matched by all the parentheses in
             the regular expression.  If there are no parentheses, it  returns
             a  list  of all the matched strings, as if there were parentheses
             around the whole pattern.   In  a  scalar  context,  it  iterates
             through  the  string,  returning  TRUE  each time it matches, and
             FALSE when it eventually runs out of matches.  (In  other  words,
             it  remembers where it left off last time and restarts the search
             at that point.)  It presumes  that  you  have  not  modified  the
             string  since  the  last  match.   Modifying  the  string between
             matches may result in undefined behavior.  (You can actually  get
             away  with in-place modifications via substr() that do not change
             the length of the entire string.  In general, however, you should
             be using s///g for such modifications.)  Examples:

                     # array context
                     ($one,$five,$fifteen) = (`uptime` =~ /(\d+\.\d+)/g);

                     # scalar context
                     $/ = ""; $* = 1;
                     while ($paragraph = <>) {
                        while ($paragraph =~ /[a-z]['")]*[.!?]+['")]*\s/g) {

                     print "$sentences\n";

             Creates the directory specified  by  FILENAME,  with  permissions
             specified  by  MODE  (as  modified  by umask).  If it succeeds it
             returns 1, otherwise it returns 0 and sets $! (errno).

             Calls the System V IPC function msgctl.   If  CMD  is  &IPC_STAT,
             then ARG must be a variable which will hold the returned msqid_ds
             structure.  Returns like ioctl: the undefined value for error, "0
             but true" for zero, or the actual return value otherwise.

             Calls the System V IPC  function  msgget.   Returns  the  message
             queue id, or the undefined value if there is an error.

             Calls the System V IPC function msgsnd to send the message MSG to
             the  message  queue  ID.   MSG  must  begin with the long integer
             message  type,  which  may  be  created  with  pack("L",  $type).
             Returns true if successful, or false if there is an error.

             Calls the System V IPC function msgrcv to receive a message  from
             message queue ID into variable VAR with a maximum message size of
             SIZE.  Note that if a message is received, the message type  will
             be  the first thing in VAR, and the maximum length of VAR is SIZE
             plus the size of the message type.  Returns true  if  successful,
             or false if there is an error.

     next LABEL

     next    The next command is like the continue statement in C;  it  starts
             the next iteration of the loop:

                     line: while (<STDIN>) {
                             next line if /^#/; # discard comments

             Note that if there were a continue block on the above,  it  would
             get  executed  even on discarded lines.  If the LABEL is omitted,
             the command refers to the innermost enclosing loop.


     oct EXPR
             Returns the decimal value of EXPR interpreted as an octal string.
             (If  EXPR  happens  to  start off with 0x, interprets it as a hex
             string instead.)  The following will handle  decimal,  octal  and
             hex in the standard notation:

                     $val = oct($val) if $val =~ /^0/;

             If EXPR is omitted, uses $_.



     open FILEHANDLE
             Opens the file whose filename is given by EXPR, and associates it
             with  FILEHANDLE.   If  FILEHANDLE is an expression, its value is
             used as the name of the  real  filehandle  wanted.   If  EXPR  is
             omitted,  the  scalar variable of the same name as the FILEHANDLE
             contains the filename.  If the  filename  begins  with  ``<''  or
             nothing,  the  file  is opened for input.  If the filename begins
             with ``>'', the file is  opened  for  output.   If  the  filename
             begins  with  ``>>'', the file is opened for appending.  (You can
             put a '+' in front of the '>' or '<' to indicate  that  you  want
             both  read and write access to the file.)  If the filename begins
             with ``|'', the filename is interpreted as  a  command  to  which
             output is to be piped, and if the filename ends with a ``|'', the
             filename is interpreted as command which pipes input to us.  (You
             may  not have a command that pipes both in and out.)  Opening '-'
             opens STDIN and opening '>-' opens STDOUT.  Open returns non-zero
             upon  success,  the  undefined  value  otherwise.   If  the  open
             involved a pipe, the return value happens to be the  pid  of  the
             subprocess.  Examples:

                     $article = 100;
                     open article || die "Can't find article $article: $!\n";
                     while (<article>) {...

                     open(LOG, '>>/usr/spool/news/twitlog');
                                                     # (log is reserved)

                     open(article, "caesar <$article |");
                                                     # decrypt article

                     open(extract, "|sort >/tmp/Tmp$$");
                                                     # $$ is our process#

                     # process argument list of files along with any includes

                     foreach $file (@ARGV) {
                             do process($file, 'fh00'); # no pun intended

                     sub process {
                             local($filename, $input) = @_;
                             $input++;       # this is a string increment
                             unless (open($input, $filename)) {
                                     print  STDERR  "Can't   open   $filename:
                             while (<$input>) { # note the use of indirection
                                     if (/^#include "(.*)"/) {
                                             do process($1, $input);
                                     ...             # whatever

             You may also, in the Bourne  shell  tradition,  specify  an  EXPR
             beginning  with  ``>&'',  in which case the rest of the string is
             interpreted as the name of a filehandle (or file  descriptor,  if
             numeric) which is to be duped and opened.  You may use & after >,
             >>, <, +>, +>> and +<.  The mode you  specify  should  match  the
             mode  of  the  original filehandle.  Here is a script that saves,
             redirects, and restores STDOUT and STDERR:

                     open(SAVEOUT, ">&STDOUT");
                     open(SAVEERR, ">&STDERR");

                     open(STDOUT, ">foo.out") || die "Can't redirect stdout";
                     open(STDERR, ">&STDOUT") || die "Can't dup stdout";

                     select(STDERR); $| = 1; # make unbuffered
                     select(STDOUT); $| = 1; # make unbuffered

                     print STDOUT "stdout 1\n"; # this works for
                     print STDERR "stderr 1\n"; # subprocesses too


                     open(STDOUT, ">&SAVEOUT");
                     open(STDERR, ">&SAVEERR");

                     print STDOUT "stdout 2\n";
                     print STDERR "stderr 2\n";

             If you open a pipe on the command ``-'', i.e.  either  ``|-''  or
             ``-|'', then there is an implicit fork done, and the return value
             of open is the pid of the child within the parent process, and  0
             within the child process.  (Use defined($pid) to determine if the
             open was successful.)  The filehandle behaves  normally  for  the
             parent,   but  i/o  to  that  filehandle  is  piped  from/to  the
             STDOUT/STDIN of the child process.   In  the  child  process  the
             filehandle  isn't opened----i/o happens from/to the new STDOUT or
             STDIN.  Typically this is used like the normal  piped  open  when
             you  want to exercise more control over just how the pipe command
             gets executed, such as when you are  running  setuid,  and  don't
             want  to  have  to  scan  shell commands for metacharacters.  The
             following pairs are more or less equivalent:

                     open(FOO, "|tr '[a-z]' '[A-Z]'");
                     open(FOO, "|-") || exec 'tr', '[a-z]', '[A-Z]';

                     open(FOO, "cat -n '$file'|");
                     open(FOO, "-|") || exec 'cat', '-n', $file;

             Explicitly closing any piped filehandle causes the parent process
             to  wait for the child to finish, and returns the status value in
             $?.  Note: on any  operation  which  may  do  a  fork,  unflushed
             buffers  remain  unflushed in both processes, which means you may
             need to set $| to avoid duplicate output.

             The filename that  is  passed  to  open  will  have  leading  and
             trailing  whitespace  deleted.   In  order  to  open  a file with
             arbitrary weird characters in it, it's necessary to  protect  any
             leading and trailing whitespace thusly:

                     $file =~ s#^(\s)#./$1#;
                     open(FOO, "< $file\0");

             Opens  a  directory  named  EXPR  for  processing  by  readdir(),
             telldir(),  seekdir(),  rewinddir() and closedir().  Returns true
             if successful.  DIRHANDLEs have their own namespace separate from


     ord EXPR
             Returns the numeric ascii value of the first character  of  EXPR.
             If EXPR is omitted, uses $_.

             Takes an array or list of values  and  packs  it  into  a  binary
             structure,  returning  the  string containing the structure.  The
             TEMPLATE is a sequence of characters that give the order and type
             of values, as follows:

                     A       An ascii string, will be space padded.
                     a       An ascii string, will be null padded.
                     c       A signed char value.
                     C       An unsigned char value.
                     s       A signed short value.
                     S       An unsigned short value.
                     i       A signed integer value.
                     I       An unsigned integer value.
                     l       A signed long value.
                     L       An unsigned long value.
                     n       A short in ``network'' order.
                     N       A long in ``network'' order.
                     f       A single-precision float in the native format.
                     d       A double-precision float in the native format.
                     p       A pointer to a string.
                     v       A short in ``VAX'' (little-endian) order.
                     V       A long in ``VAX'' (little-endian) order.
                     x       A null byte.
                     X       Back up a byte.
                     @       Null fill to absolute position.
                     u       A uuencoded string.
                     b       A bit string (ascending bit order, like vec()).
                     B       A bit string (descending bit order).
                     h       A hex string (low nybble first).
                     H       A hex string (high nybble first).

             Each letter may optionally be followed by a number which gives  a
             repeat  count.  With all types except "a", "A", "b", "B", "h" and
             "H", the pack function will gobble up that many values  from  the
             LIST.   A  * for the repeat count means to use however many items
             are left.  The "a" and "A" types gobble just one value, but  pack
             it  as  a string of length count, padding with nulls or spaces as
             necessary.  (When  unpacking,  "A"  strips  trailing  spaces  and
             nulls,  but "a" does not.)  Likewise, the "b" and "B" fields pack
             a string that many bits long.  The "h"  and  "H"  fields  pack  a
             string that many nybbles long.  Real numbers (floats and doubles)
             are in the native machine format only; due to the multiplicity of
             floating  formats  around, and the lack of a standard ``network''
             representation, no facility for interchange has been made.   This
             means  that packed floating point data written on one machine may
             not be readable on another - even if both use IEEE floating point
             arithmetic  (as  the  endian-ness of the memory representation is
             not part  of  the  IEEE  spec).   Note  that  perl  uses  doubles
             internally  for  all  numeric  calculation,  and  converting from
             double -> float -> double will lose precision  (i.e.  unpack("f",
             pack("f", $foo)) will not in general equal $foo).

                     $foo = pack("cccc",65,66,67,68);
                     # foo eq "ABCD"
                     $foo = pack("c4",65,66,67,68);
                     # same thing

                     $foo = pack("ccxxcc",65,66,67,68);
                     # foo eq "AB\0\0CD"

                     $foo = pack("s2",1,2);
                     # "\1\0\2\0" on little-endian
                     # "\0\1\0\2" on big-endian

                     $foo = pack("a4","abcd","x","y","z");
                     # "abcd"

                     $foo = pack("aaaa","abcd","x","y","z");
                     # "axyz"

                     $foo = pack("a14","abcdefg");
                     # "abcdefg\0\0\0\0\0\0\0"

                     $foo = pack("i9pl", gmtime);
                     # a real struct tm (on my system anyway)

                     sub bintodec {
                        unpack("N",  pack("B32",  substr("0"  x  32  .  shift,

             The same template may  generally  also  be  used  in  the  unpack

             Opens a pair of connected pipes  like  the  corresponding  system
             call.   Note  that  if  you  set  up  a  loop of piped processes,
             deadlock can occur unless you are  very  careful.   In  addition,
             note  that  perl's  pipes use stdio buffering, so you may need to
             set $| to flush your WRITEHANDLE after each command, depending on
             the application.  [Requires version 3.0 patchlevel 9.]


     pop ARRAY
             Pops and returns the last value  of  the  array,  shortening  the
             array by 1.  Has the same effect as

                     $tmp = $ARRAY[$#ARRAY--];

             If there are no elements in  the  array,  returns  the  undefined




     print LIST

     print   Prints a string or a comma-separated list  of  strings.   Returns
             non-zero  if  successful.   FILEHANDLE  may  be a scalar variable
             name, in which  case  the  variable  contains  the  name  of  the
             filehandle, thus introducing one level of indirection.  (NOTE: If
             FILEHANDLE is a variable and the next token is a term, it may  be
             misinterpreted  as  an  operator  unless you interpose a + or put
             parens around the arguments.)  If FILEHANDLE is  omitted,  prints
             by  default  to  standard  output (or to the last selected output
             channel----see select()).  If LIST is also omitted, prints $_  to
             STDOUT.   To  set  the  default output channel to something other
             than STDOUT use the select operation.  Note that,  because  print
             takes  a  LIST,  anything  in  the  LIST is evaluated in an array
             context, and any subroutine that you call will have one  or  more
             of  its  expressions  evaluated  in  an  array  context.  Also be
             careful not to follow the print keyword with a  left  parenthesis
             unless  you want the corresponding right parenthesis to terminate
             the arguments to the print----interpose a + or put parens  around
             all the arguments.

     printf(FILEHANDLE LIST)



     printf LIST
             Equivalent to a ``print FILEHANDLE sprintf(LIST)''.

             Treats ARRAY (@ is optional) as a stack, and pushes the values of
             LIST onto the end of ARRAY.  The length of ARRAY increases by the
             length of LIST.  Has the same effect as

                 for $value (LIST) {
                        $ARRAY[++$#ARRAY] = $value;

             but is more efficient.



             These are not really functions, but simply syntactic sugar to let
             you  avoid putting too many backslashes into quoted strings.  The
             q operator is a generalized single quote, and the qq  operator  a
             generalized  double  quote.   The  qx  operator  is a generalized
             backquote.  Any non-alphanumeric delimiter can be used  in  place
             of  /, including newline.  If the delimiter is an opening bracket
             or parenthesis, the final delimiter  will  be  the  corresponding
             closing  bracket  or  parenthesis.   (Embedded occurrences of the
             closing bracket need to be backslashed as usual.)  Examples:

                     $foo = q!I said, "You said, 'She said it.'"!;
                     $bar = q('This is it.');
                     $today = qx{ date };
                     $_ .= qq
             *** The previous line contains the naughty word "$&".\n
                             if /(ibm|apple|awk)/;      # :-)


     rand EXPR

     rand    Returns a random fractional number between 0  and  the  value  of
             EXPR.   (EXPR should be positive.)  If EXPR is omitted, returns a
             value between 0 and 1.  See also srand().


             Attempts to read LENGTH bytes of data into variable  SCALAR  from
             the  specified  FILEHANDLE.  Returns the number of bytes actually
             read, or undef if there was an error.  SCALAR will  be  grown  or
             shrunk  to  the length actually read.  An OFFSET may be specified
             to place the read data at some other place than the beginning  of
             the  string.   This  call  is  actually  implemented  in terms of
             stdio's fread call.  To get a true read system call, see sysread.


     readdir DIRHANDLE
             Returns the next  directory  entry  for  a  directory  opened  by
             opendir().   If used in an array context, returns all the rest of
             the entries in the directory.  If  there  are  no  more  entries,
             returns  an undefined value in a scalar context or a null list in
             an array context.


     readlink EXPR
             Returns the value of a  symbolic  link,  if  symbolic  links  are
             implemented.   If  not,  gives  a  fatal error.  If there is some
             system error, returns the undefined value and  sets  $!  (errno).
             If EXPR is omitted, uses $_.

             Receives a message on a socket.  Attempts to receive LENGTH bytes
             of   data   into   variable  SCALAR  from  the  specified  SOCKET
             filehandle.  Returns the address of the sender, or the  undefined
             value if there's an error.  SCALAR will be grown or shrunk to the
             length actually read.  Takes the same flags as the system call of
             the same name.

     redo LABEL

     redo    The redo command restarts the loop block without  evaluating  the
             conditional  again.  The continue block, if any, is not executed.
             If the LABEL is omitted, the  command  refers  to  the  innermost
             enclosing  loop.   This command is normally used by programs that
             want to lie to themselves about what was just input:

                     # a simpleminded Pascal comment stripper
                     # (warning: assumes no { or } in strings)
                     line: while (<STDIN>) {
                             while (s|({.*}.*){.*}|$1 |) {}
                             s|{.*}| |;
                             if (s|{.*| |) {
                                     $front = $_;
                                     while (<STDIN>) {
                                             if (/}/) { # end of comment?
                                                     redo line;

             Changes the name of a file.  Returns 1 for success, 0  otherwise.
             Will not work across filesystem boundaries.


     require EXPR

     require Includes the library file specified by EXPR, or by $_ if EXPR  is
             not supplied.  Has semantics similar to the following subroutine:

                     sub require {
                        local($filename) = @_;
                        return 1 if $INC{$filename};
                        ITER: {
                             foreach $prefix (@INC) {
                                $realfilename = "$prefix/$filename";
                                if (-f $realfilename) {
                                     $result = do $realfilename;
                                     last ITER;
                             die "Can't find $filename in \@INC";
                        die $@ if $@;
                        die "$filename  did  not  return  true  value"  unless
                        $INC{$filename} = $realfilename;

             Note that the file will not be  included  twice  under  the  same
             specified  name.  The file must return true as the last statement
             to indicate successful execution of any initialization  code,  so
             it's  customary to end such a file with ``1;'' unless you're sure
             it'll return true otherwise.


     reset EXPR

     reset   Generally used in a continue block at the end of a loop to  clear
             variables  and  reset  ??  searches so that they work again.  The
             expression is interpreted as a list of single characters (hyphens
             allowed for ranges).  All variables and arrays beginning with one
             of those letters are reset  to  their  pristine  state.   If  the
             expression  is  omitted, one-match searches (?pattern?) are reset
             to match again.  Only resets variables or searches in the current
             package.  Always returns 1.  Examples:

                 reset 'X';          # reset all X variables
                 reset 'a-z';        # reset lower case variables
                 reset;              # just reset ?? searches

             Note: resetting ``A-Z'' is not recommended since you'll wipe  out
             your ARGV and ENV arrays.

             The use of reset on dbm associative arrays does  not  change  the
             dbm  file.   (It does, however, flush any entries cached by perl,
             which may be useful if you are sharing the dbm file.  Then again,
             maybe not.)

     return LIST
             Returns from a subroutine with the value specified.  (Note that a
             subroutine  can  automatically  return  the  value  of  the  last
             expression evaluated.  That's the preferred method----use  of  an
             explicit return is a bit slower.)


     reverse LIST
             In an array context, returns an array  value  consisting  of  the
             elements  of  LIST  in  the opposite order.  In a scalar context,
             returns a string value consisting  of  the  bytes  of  the  first
             element of LIST in the opposite order.


     rewinddir DIRHANDLE
             Sets the current position to the beginning of the  directory  for
             the readdir() routine on DIRHANDLE.


             Works just like index except that it returns the position of  the
             LAST  occurrence  of  SUBSTR  in  STR.  If POSITION is specified,
             returns the last occurrence at or before that position.


     rmdir FILENAME
             Deletes the directory specified by FILENAME if it is  empty.   If
             it  succeeds  it  returns  1,  otherwise it returns 0 and sets $!
             (errno).  If FILENAME is omitted, uses $_.

             Searches a string for a pattern,  and  if  found,  replaces  that
             pattern  with  the  replacement  text  and  returns the number of
             substitutions made.  Otherwise it returns false (0).   The  ``g''
             is  optional,  and  if present, indicates that all occurrences of
             the pattern are to be replaced.  The ``i'' is also optional,  and
             if  present,  indicates  that  matching  is to be done in a case-
             insensitive manner.  The  ``e''  is  likewise  optional,  and  if
             present, indicates that the replacement string is to be evaluated
             as an expression rather than just as a double-quoted string.  Any
             non-alphanumeric  delimiter  may  replace  the slashes; if single
             quotes are used, no interpretation is  done  on  the  replacement
             string  (the  e  modifier overrides this, however); if backquotes
             are used, the replacement string is a command  to  execute  whose
             output  will  be  used  as  the  actual replacement text.  If the
             PATTERN is delimited by bracketing quotes,  the  REPLACEMENT  has
             its  own  pair  of  quotes,  which  may  or may not be bracketing
             quotes, e.g.   s(foo)(bar)  or  s<foo>/bar/.   If  no  string  is
             specified  via  the  =~ or !~ operator, the $_ string is searched
             and modified.  (The string specified with =~  must  be  a  scalar
             variable,  an  array  element,  or an assignment to one of those,
             i.e. an lvalue.)  If the pattern contains a $ that looks  like  a
             variable  rather than an end-of-string test, the variable will be
             interpolated into the pattern at run-time.  If you only want  the
             pattern   compiled   once   the   first   time  the  variable  is
             interpolated, add an ``o'' at the end.  If the PATTERN  evaluates
             to  a  null string, the most recent successful regular expression
             is used instead.  See also the section  on  regular  expressions.

                 s/\bgreen\b/mauve/g; # don't change wintergreen

                 $path =~ s|/usr/bin|/usr/local/bin|;

                 s/Login: $foo/Login: $bar/; # run-time pattern

                 ($foo = $bar) =~ s/bar/foo/;

                 $_ = 'abc123xyz';
                 s/\d+/$&*2/e; # yields `abc246xyz'
                 s/\d+/sprintf("%5d",$&)/e; # yields `abc  246xyz'
                 s/\w/$& x 2/eg; # yields `aabbcc  224466xxyyzz'

                 s/([^ ]*) *([^ ]*)/$2 $1/; # reverse 1st two fields

             (Note the use of $ instead of \ in the last example.  See section
             on regular expressions.)

             Forces EXPR to be interpreted in a scalar context and returns the
             value of EXPR.

             Randomly positions the file pointer for FILEHANDLE, just like the
             fseek()  call  of  stdio.   FILEHANDLE may be an expression whose
             value gives the name of the filehandle.  Returns 1 upon  success,
             0 otherwise.

             Sets the current position for the readdir() routine on DIRHANDLE.
             POS  must be a value returned by telldir().  Has the same caveats
             about possible directory compaction as the  corresponding  system
             library routine.


     select  Returns the currently  selected  filehandle.   Sets  the  current
             default  filehandle  for output, if FILEHANDLE is supplied.  This
             has two effects: first, a write or a print without  a  filehandle
             will default to this FILEHANDLE.  Second, references to variables
             related to  output  will  refer  to  this  output  channel.   For
             example,  if you have to set the top of form format for more than
             one output channel, you might do the following:

                     $^ = 'report1_top';
                     $^ = 'report2_top';

             FILEHANDLE may be an expression whose value gives the name of the
             actual filehandle.  Thus:

                     $oldfh = select(STDERR); $| = 1; select($oldfh);

             This calls the select system call with  the  bitmasks  specified,
             which  can  be  constructed using fileno() and vec(), along these

                     $rin = $win = $ein = '';
                     vec($rin,fileno(STDIN),1) = 1;
                     vec($win,fileno(STDOUT),1) = 1;
                     $ein = $rin | $win;

             If you want to select on many filehandles you might wish to write
             a subroutine:

                     sub fhbits {
                        local(@fhlist) = split(' ',$_[0]);
                        for (@fhlist) {
                             vec($bits,fileno($_),1) = 1;
                     $rin = &fhbits('STDIN TTY SOCK');

             The usual idiom is:

                     ($nfound,$timeleft) =
                      select($rout=$rin, $wout=$win, $eout=$ein, $timeout);

             or to block until something becomes ready:

                     $nfound = select($rout=$rin, $wout=$win,
                                             $eout=$ein, undef);

             Any  of  the  bitmasks  can  also  be  undef.   The  timeout,  if
             specified, is in seconds, which may be fractional.  NOTE: not all
             implementations are capable of returning the $timeleft.  If  not,
             they always return $timeleft equal to the supplied $timeout.

             Calls the System V IPC function semctl.  If CMD is  &IPC_STAT  or
             &GETALL, then ARG must be a variable which will hold the returned
             semid_ds structure or semaphore value array.  Returns like ioctl:
             the  undefined  value  for  error,  "0 but true" for zero, or the
             actual return value otherwise.

             Calls the System V IPC function semget.   Returns  the  semaphore
             id, or the undefined value if there is an error.

             Calls the System  V  IPC  function  semop  to  perform  semaphore
             operations  such  as  signaling  and waiting.  OPSTRING must be a
             packed array of semop structures.  Each semop  structure  can  be
             generated  with  'pack("sss",  $semnum,  $semop, $semflag)'.  The
             number of semaphore  operations  is  implied  by  the  length  of
             OPSTRING.   Returns  true  if successful, or false if there is an
             error.  As an example, the  following  code  waits  on  semaphore
             $semnum of semaphore id $semid:

                     $semop = pack("sss", $semnum, -1, 0);
                     die  "Semaphore  trouble:  $!\n"   unless   semop($semid,

             To signal the semaphore, replace "-1" with "1".


             Sends a message on a socket.  Takes the same flags as the  system
             call of the same name.  On unconnected sockets you must specify a
             destination to send TO.  Returns the number of  characters  sent,
             or the undefined value if there is an error.

             Sets the current process group for the specified PID, 0  for  the
             current process.  Will produce a fatal error if used on a machine
             that doesn't implement setpgrp(2).

             Sets the current priority for a process, a process  group,  or  a
             user.   (See setpriority(2).)  Will produce a fatal error if used
             on a machine that doesn't implement setpriority(2).

             Sets the socket option requested.  Returns undefined if there  is
             an  error.  OPTVAL may be specified as undef if you don't want to
             pass an argument.


     shift ARRAY

     shift   Shifts  the  first  value  of  the  array  off  and  returns  it,
             shortening  the  array by 1 and moving everything down.  If there
             are no elements in the array, returns the  undefined  value.   If
             ARRAY is omitted, shifts the @ARGV array in the main program, and
             the @_ array in subroutines.   (This  is  determined  lexically.)
             See  also  unshift(), push() and pop().  Shift() and unshift() do
             the same thing to the left end of an array that push() and  pop()
             do to the right end.

             Calls the System V IPC function shmctl.   If  CMD  is  &IPC_STAT,
             then ARG must be a variable which will hold the returned shmid_ds
             structure.  Returns like ioctl: the undefined value for error, "0
             but true" for zero, or the actual return value otherwise.

             Calls the System V  IPC  function  shmget.   Returns  the  shared
             memory segment id, or the undefined value if there is an error.


             Reads or writes the System V shared memory segment ID starting at
             position  POS  for  size SIZE by attaching to it, copying in/out,
             and detaching from it.  When reading,  VAR  must  be  a  variable
             which  will  hold  the data read.  When writing, if STRING is too
             long, only SIZE bytes are used; if STRING is too short, nulls are
             written  to  fill  out SIZE bytes.  Return true if successful, or
             false if there is an error.

             Shuts down a socket connection in the manner  indicated  by  HOW,
             which  has  the  same interpretation as in the system call of the
             same name.


     sin EXPR
             Returns the sine of EXPR (expressed  in  radians).   If  EXPR  is
             omitted, returns sine of $_.


     sleep EXPR

     sleep   Causes the script to sleep for EXPR seconds,  or  forever  if  no
             EXPR.   May  be  interrupted  by  sending  the process a SIGALRM.
             Returns the number  of  seconds  actually  slept.   You  probably
             cannot  mix  alarm()  and  sleep()  calls, since sleep() is often
             implemented using alarm().

             Opens  a  socket  of  the  specified  kind  and  attaches  it  to
             filehandle  SOCKET.   DOMAIN, TYPE and PROTOCOL are specified the
             same as for the system call of the same name.  You  may  need  to
             run h2ph on sys/socket.h to get the proper values handy in a perl
             library file.  Return true if successful.  See the example in the
             section on Interprocess Communication.

             Creates an unnamed pair of sockets in the  specified  domain,  of
             the  specified type.  DOMAIN, TYPE and PROTOCOL are specified the
             same as for the system call of the same name.  If  unimplemented,
             yields a fatal error.  Return true if successful.




     sort BLOCK LIST

     sort LIST
             Sorts the LIST and returns the sorted array  value.   Nonexistent
             values  of  arrays  are  stripped out.  If SUBROUTINE or BLOCK is
             omitted,  sorts  in  standard  string   comparison   order.    If
             SUBROUTINE  is  specified,  gives  the  name of a subroutine that
             returns an integer less  than,  equal  to,  or  greater  than  0,
             depending  on  how  the  elements of the array are to be ordered.
             (The  <=>  and  cmp  operators  are  extremely  useful  in   such
             routines.)   SUBROUTINE  may  be a scalar variable name, in which
             case the value provides the name of the subroutine  to  use.   In
             place  of  a  SUBROUTINE  name,  you  can  provide  a BLOCK as an
             anonymous, in-line sort subroutine.

             In the interests  of  efficiency  the  normal  calling  code  for
             subroutines   is   bypassed,  with  the  following  effects:  the
             subroutine may  not  be  a  recursive  subroutine,  and  the  two
             elements to be compared are passed into the subroutine not via @_
             but as $a and  $b  (see  example  below).   They  are  passed  by
             reference so don't modify $a and $b.


                     # sort lexically
                     @articles = sort @files;

                     # same thing, but with explicit sort routine
                     @articles = sort {$a cmp $b} @files;

                     # same thing in reversed order
                     @articles = sort {$b cmp $a} @files;

                     # sort numerically ascending
                     @articles = sort {$a <=> $b} @files;

                     # sort numerically descending
                     @articles = sort {$b <=> $a} @files;

                     # sort using explicit subroutine name
                     sub byage {
                        $age{$a} <=> $age{$b}; # presuming integers
                     @sortedclass = sort byage @class;

                     sub reverse { $b cmp $a; }
                     @harry = ('dog','cat','x','Cain','Abel');
                     @george = ('gone','chased','yz','Punished','Axed');
                     print sort @harry;
                             # prints AbelCaincatdogx
                     print sort reverse @harry;
                             # prints xdogcatCainAbel
                     print sort @george, 'to', @harry;
                             #                                          prints



             Removes the elements designated by  OFFSET  and  LENGTH  from  an
             array,  and  replaces  them  with  the  elements of LIST, if any.
             Returns the elements removed from the array.  The array grows  or
             shrinks  as  necessary.  If LENGTH is omitted, removes everything
             from OFFSET onward.  The following equivalencies  hold  (assuming
             $[ == 0):

                      pop(@a)                          splice(@a,-1)
                      shift(@a)                        splice(@a,0,1)
                      unshift(@a,$x,$y)                splice(@a,0,0,$x,$y)
                      $a[$x] = $y                      splice(@a,$x,1,$y);

             Example, assuming array lengths are passed before arrays:

                     sub aeq { # compare two array values
                             local(@a) = splice(@_,0,shift);
                             local(@b) = splice(@_,0,shift);
                             return 0 unless @a == @b; # same len?
                             while (@a) {
                                return 0 if pop(@a) ne pop(@b);
                             return 1;
                     if (&aeq($len,@foo[1..$len],0+@bar,@bar)) { ... }




     split   Splits a string into an array of strings, and  returns  it.   (If
             not  in  an array context, returns the number of fields found and
             splits into the @_ array.  (In an array context,  you  can  force
             the  split  into @_ by using ?? as the pattern delimiters, but it
             still returns the array value.))  If EXPR is omitted, splits  the
             $_  string.   If  PATTERN  is  also omitted, splits on whitespace
             (/[ \t\n]+/).   Anything  matching  PATTERN  is  taken  to  be  a
             delimiter separating the fields.  (Note that the delimiter may be
             longer than one character.)  If LIMIT is specified,  splits  into
             no  more  than that many fields (though it may split into fewer).
             If LIMIT is unspecified, trailing null fields are stripped (which
             potential  users  of pop() would do well to remember).  A pattern
             matching the null string (not to be confused with a null  pattern
             //,  which  is  just one member of the set of patterns matching a
             null  string)  will  split  the  value  of  EXPR  into   separate
             characters at each point it matches that way.  For example:

                     print join(':', split(/ */, 'hi there'));

             produces the output `h:i:t:h:e:r:e'.

             The LIMIT parameter can be used to partially split a line

                     ($login, $passwd, $remainder) = split(/:/, $_, 3);

             (When assigning to a list, if LIMIT is omitted, perl  supplies  a
             LIMIT  one  larger  than  the number of variables in the list, to
             avoid unnecessary work.  For the list above LIMIT would have been
             4  by default.  In time critical applications it behooves you not
             to split into more fields than you really need.)

             If the PATTERN contains parentheses,  additional  array  elements
             are created from each matching substring in the delimiter.


             produces the array value


             The pattern /PATTERN/ may  be  replaced  with  an  expression  to
             specify   patterns   that   vary  at  runtime.   (To  do  runtime
             compilation only once, use /$variable/o.)   As  a  special  case,
             specifying  a space (' ') will split on white space just as split
             with no arguments does, but leading white space does NOT  produce
             a  null  first  field.   Thus,  split(' ') can be used to emulate
             awk's default behavior, whereas split(/ /) will give you as  many
             null initial fields as there are leading spaces.


                     open(passwd, '/etc/passwd');
                     while (<passwd>) {
                             ($login,  $passwd,  $uid,  $gid,  $gcos,   $home,
                                     = split(/:/);

             (Note that $shell above will still have a  newline  on  it.   See
             chop().)  See also join.

             Returns a string formatted by the usual printf conventions.   The
             * character is not supported.


     sqrt EXPR
             Return the square root of EXPR.   If  EXPR  is  omitted,  returns
             square root of $_.


     srand EXPR
             Sets the random number seed for the rand operator.   If  EXPR  is
             omitted, does srand(time).


     stat FILEHANDLE


             Returns a 13-element array giving  the  statistics  for  a  file,
             either the file opened via FILEHANDLE, or named by EXPR.  Returns
             a null list if the stat fails.  Typically used as follows:

                        = stat($filename);

             If stat  is  passed  the  special  filehandle  consisting  of  an
             underline,  no stat is done, but the current contents of the stat
             structure from the last stat or filetest are returned.  Example:

                     if (-x $file && (($d) = stat(_)) && $d < 0) {
                             print "$file is executable NFS file\n";

             (This only works on machines  for  which  the  device  number  is
             negative under NFS.)


     study SCALAR

     study   Takes  extra  time  to  study  SCALAR  ($_  if  unspecified)   in
             anticipation  of  doing many pattern matches on the string before
             it is next modified.  This may or may not save time, depending on
             the  nature  and  number of patterns you are searching on, and on
             the distribution of character frequencies in  the  string  to  be
             searched----you  probably  want  to  compare  runtimes  with  and
             without it to see which runs faster.  Those loops which scan  for
             many short constant strings (including the constant parts of more
             complex patterns) will benefit most.  You may have only one study
             active  at a time----if you study a different scalar the first is
             ``unstudied''.  (The way study works is this: a  linked  list  of
             every character in the string to be searched is made, so we know,
             for example, where all the `k' characters are.  From each  search
             string,  the  rarest  character is selected, based on some static
             frequency tables constructed from some  C  programs  and  English
             text.   Only  those places that contain this ``rarest'' character
             are examined.)

             For example, here is a loop which inserts index producing entries
             before any line containing a certain pattern:

                     while (<>) {
                             print ".IX foo\n" if /\bfoo\b/;
                             print ".IX bar\n" if /\bbar\b/;
                             print ".IX blurfl\n" if /\bblurfl\b/;

             In searching for /\bfoo\b/,  only  those  locations  in  $_  that
             contain `f' will be looked at, because `f' is rarer than `o'.  In
             general, this is a big win except  in  pathological  cases.   The
             only  question  is whether it saves you more time than it took to
             build the linked list in the first place.

             Note that if you have to look for strings  that  you  don't  know
             till  runtime,  you can build an entire loop as a string and eval
             that to  avoid  recompiling  all  your  patterns  all  the  time.
             Together  with undefining $/ to input entire files as one record,
             this can be very fast, often  faster  than  specialized  programs
             like  fgrep.   The following scans a list of files (@files) for a
             list of words (@words), and prints out the names of  those  files
             that contain a match:

                     $search = 'while (<>) { study;';
                     foreach $word (@words) {
                        $search .= "++\$seen{\$ARGV} if /\\b$word\\b/;\n";
                     $search .= "}";
                     @ARGV = @files;
                     undef $/;
                     eval $search;   # this screams
                     $/ = "\n";      # put back to normal input delim
                     foreach $file (sort keys(%seen)) {
                        print $file, "\n";


             Extracts a substring out of EXPR and returns it.  First character
             is  at  offset  0,  or  whatever  you've set $[ to.  If OFFSET is
             negative, starts that far from the end of the string.  If LEN  is
             omitted,  returns  everything  to the end of the string.  You can
             use the substr() function as an lvalue, in which case  EXPR  must
             be  an  lvalue.   If  you  assign something shorter than LEN, the
             string will shrink, and if you assign something longer than  LEN,
             the  string  will grow to accommodate it.  To keep the string the
             same length you  may  need  to  pad  or  chop  your  value  using

             Creates a new filename symbolically linked to the  old  filename.
             Returns  1  for  success,  0  otherwise.   On  systems that don't
             support symbolic links, produces a fatal error at run  time.   To
             check for that, use eval:

                     $symlink_exists = (eval 'symlink("","");', $@ eq '');


     syscall LIST
             Calls the system call specified as the first element of the list,
             passing  the  remaining elements as arguments to the system call.
             If unimplemented, produces a  fatal  error.   The  arguments  are
             interpreted  as  follows:  if  a  given  argument is numeric, the
             argument is passed as an int.  If not, the pointer to the  string
             value  is  passed.   You are responsible to make sure a string is
             pre-extended long enough to receive  any  result  that  might  be
             written  into  a  string.   If  your  integer  arguments  are not
             literals and have never been interpreted in  a  numeric  context,
             you may need to add 0 to them to force them to look like numbers.

                     require ''; # may need to run h2ph
                     syscall(&SYS_write, fileno(STDOUT), "hi there\n", 9);


             Attempts to read LENGTH bytes of data into variable  SCALAR  from
             the  specified  FILEHANDLE,  using  the  system call read(2).  It
             bypasses stdio, so mixing this with  other  kinds  of  reads  may
             cause  confusion.   Returns the number of bytes actually read, or
             undef if there was an error.  SCALAR will be grown or  shrunk  to
             the  length  actually  read.  An OFFSET may be specified to place
             the read data at some other  place  than  the  beginning  of  the


     system LIST
             Does exactly the same thing as ``exec LIST'' except that  a  fork
             is done first, and the parent process waits for the child process
             to complete.  Note that argument processing varies  depending  on
             the  number of arguments.  The return value is the exit status of
             the program as returned by the wait() call.  To  get  the  actual
             exit value divide by 256.  See also exec.


             Attempts to write LENGTH bytes of data from  variable  SCALAR  to
             the  specified  FILEHANDLE,  using  the system call write(2).  It
             bypasses stdio, so mixing this with prints may  cause  confusion.
             Returns  the  number of bytes actually written, or undef if there
             was an error.  An OFFSET may be specified to place the read  data
             at some other place than the beginning of the string.


     tell FILEHANDLE

     tell    Returns the current file position for FILEHANDLE.  FILEHANDLE may
             be  an  expression  whose  value  gives  the  name  of the actual
             filehandle.  If FILEHANDLE is  omitted,  assumes  the  file  last


     telldir DIRHANDLE
             Returns  the  current  position  of  the  readdir()  routines  on
             DIRHANDLE.    Value  may  be  given  to  seekdir()  to  access  a
             particular location in a directory.  Has the same  caveats  about
             possible directory compaction as the corresponding system library

     time    Returns the  number  of  non-leap  seconds  since  00:00:00  UTC,
             January   1,   1970.    Suitable  for  feeding  to  gmtime()  and

     times   Returns a four-element array giving the user and system times, in
             seconds, for this process and the children of this process.

                 ($user,$system,$cuser,$csystem) = times;


             Translates all occurrences of the characters found in the  search
             list  with  the  corresponding character in the replacement list.
             It returns the number of characters replaced or deleted.   If  no
             string  is  specified via the =~ or !~ operator, the $_ string is
             translated.  (The string specified  with  =~  must  be  a  scalar
             variable,  an  array  element,  or an assignment to one of those,
             i.e. an lvalue.)  For sed devotees, y is provided  as  a  synonym
             for tr.  If the SEARCHLIST is delimited by bracketing quotes, the
             REPLACEMENTLIST has its own pair of quotes, which may or may  not
             be bracketing quotes, e.g.  tr[A-Z][a-z] or tr(+-*/)/ABCD/.

             If the c modifier is specified, the SEARCHLIST character  set  is
             complemented.   If  the  d  modifier is specified, any characters
             specified by SEARCHLIST that are not found in REPLACEMENTLIST are
             deleted.   (Note  that  this  is  slightly more flexible than the
             behavior of some tr programs, which delete anything they find  in
             the  SEARCHLIST,  period.)   If  the  s  modifier  is  specified,
             sequences  of  characters  that  were  translated  to  the   same
             character are squashed down to 1 instance of the character.

             If the  d  modifier  was  used,  the  REPLACEMENTLIST  is  always
             interpreted    exactly   as   specified.    Otherwise,   if   the
             REPLACEMENTLIST  is  shorter  than  the  SEARCHLIST,  the   final
             character   is  replicated  till  it  is  long  enough.   If  the
             REPLACEMENTLIST is null,  the  SEARCHLIST  is  replicated.   This
             latter  is  useful  for  counting  characters  in a class, or for
             squashing character sequences in a class.


                 $ARGV[1] =~ y/A-Z/a-z/;         # canonicalize to lower case

                 $cnt = tr/*/*/;                 # count the stars in $_

                 $cnt = tr/0-9//;                # count the digits in $_

                 tr/a-zA-Z//s;                   # bookkeeper -> bokeper

                 ($HOST = $host) =~ tr/a-z/A-Z/;

                 y/a-zA-Z/ /cs;                  # change non-alphas to single

                 tr/\200-\377/\0-\177/;          # delete 8th bit


             Truncates the file opened on FILEHANDLE, or named by EXPR, to the
             specified  length.   Produces  a  fatal  error  if truncate isn't
             implemented on your system.


     umask EXPR

     umask   Sets the umask for the process and returns the old one.  If  EXPR
             is omitted, merely returns current umask.


     undef EXPR

     undef   Undefines the value of EXPR, which must be an lvalue.   Use  only
             on  a  scalar value, an entire array, or a subroutine name (using
             &).  (Undef  will  probably  not  do  what  you  expect  on  most
             predefined  variables  or  dbm array values.)  Always returns the
             undefined value.  You can omit the EXPR, in which case nothing is
             undefined,  but  you still get an undefined value that you could,
             for instance, return from a subroutine.  Examples:

                     undef $foo;
                     undef $bar{'blurfl'};
                     undef @ary;
                     undef %assoc;
                     undef &mysub;
                     return (wantarray ? () : undef) if $they_blew_it;


     unlink LIST
             Deletes  a  list  of  files.   Returns  the   number   of   files
             successfully deleted.

                     $cnt = unlink 'a', 'b', 'c';
                     unlink @goners;
                     unlink <*.bak>;

             Note: unlink will not delete directories unless you are superuser
             and  the  -U  flag is supplied to perl.  Even if these conditions
             are met, be warned that unlinking a directory can inflict  damage
             on your filesystem.  Use rmdir instead.

             Unpack does the reverse of pack: it takes a string representing a
             structure  and  expands it out into an array value, returning the
             array value.  (In a scalar context, it merely returns  the  first
             value produced.)  The TEMPLATE has the same format as in the pack
             function.  Here's a subroutine that does substring:

                     sub substr {
                             local($what,$where,$howmuch) = @_;
                             unpack("x$where a$howmuch", $what);

             and then there's

                     sub ord { unpack("c",$_[0]); }

             In addition, you may prefix a field with a %<number> to  indicate
             that you want a <number>-bit checksum of the items instead of the
             items themselves.  Default is a 16-bit  checksum.   For  example,
             the  following  computes  the  same  number  as  the System V sum

                     while (<>) {
                        $checksum += unpack("%16C*", $_);
                     $checksum %= 65536;

             Does the opposite of  a  shift.   Or  the  opposite  of  a  push,
             depending  on  how you look at it.  Prepends list to the front of
             the array, and returns the number of elements in the new array.

                     unshift(ARGV, '-e') unless $ARGV[0] =~ /^-/;


     utime LIST
             Changes the access and modification times on each file of a  list
             of  files.   The  first  two  elements  of  the  list must be the
             NUMERICAL access and modification times, in that order.   Returns
             the number of files successfully changed.  The inode modification
             time of each file is set to  the  current  time.   Example  of  a
             ``touch'' command:

                     $now = time;
                     utime $now, $now, @ARGV;


     values ASSOC_ARRAY
             Returns a normal array consisting of all the values of the  named
             associative  array.   The  values  are  returned in an apparently
             random order, but it is the same order as either  the  keys()  or
             each() function would produce on the same array.  See also keys()
             and each().

             Treats a string as a vector of unsigned integers, and returns the
             value  of the bitfield specified.  May also be assigned to.  BITS
             must be a power of two from 1 to 32.

             Vectors created with vec()  can  also  be  manipulated  with  the
             logical  operators  |,  &  and  ^, which will assume a bit vector
             operation is  desired  when  both  operands  are  strings.   This
             interpretation  is not enabled unless there is at least one vec()
             in your program, to protect older programs.

             To transform a bit vector into a string or array of 0's and  1's,
             use these:

                     $bits = unpack("b*", $vector);
                     @bits = split(//, unpack("b*", $vector));

             If you know the exact length in bits, it can be used in place  of
             the *.

     wait    Waits for a child process to terminate and returns the pid of the
             deceased  process,  or  -1  if there are no child processes.  The
             status is returned in $?.

             Waits for a particular child process to terminate and returns the
             pid  of  the  deceased  process,  or -1 if there is no such child
             process.  The status is returned in $?.  If you say

                     require "sys/wait.h";

             then you can do  a  non-blocking  wait  for  any  process.   Non-
             blocking wait is only available on machines supporting either the
             waitpid (2) or wait4 (2) system calls.  However,  waiting  for  a
             particular  pid with FLAGS of 0 is implemented everywhere.  (Perl
             emulates the system call by  remembering  the  status  values  of
             processes  that  have  exited  but have not been harvested by the
             Perl script yet.)

             Returns true if the context of the currently executing subroutine
             is  looking  for an array value.  Returns false if the context is
             looking for a scalar.

                     return wantarray ? () : undef;


     warn LIST
             Produces a message on STDERR just like ``die'', but doesn't exit.



     write   Writes a formatted record (possibly multi-line) to the  specified
             file, using the format associated with that file.  By default the
             format for a file  is  the  one  having  the  same  name  is  the
             filehandle,  but  the  format for the current output channel (see
             select) may be set explicitly by assigning the name of the format
             to the $~ variable.

             Top of form processing is handled  automatically:   if  there  is
             insufficient  room  on the current page for the formatted record,
             the page is advanced by writing a form feed,  a  special  top-of-
             page  format  is used to format the new page header, and then the
             record is written.  By default the top-of-page format is the name
             of   the  filehandle  with  ``_TOP''  appended,  but  it  may  be
             dynamicallly set to the format of your choice  by  assigning  the
             name  to  the  $^ variable while the filehandle is selected.  The
             number of lines remaining on the current page is in variable  $-,
             which can be set to 0 to force a new page.

             If FILEHANDLE is unspecified, output goes to the current  default
             output  channel, which starts out as STDOUT but may be changed by
             the select operator.  If the FILEHANDLE  is  an  EXPR,  then  the
             expression  is evaluated and the resulting string is used to look
             up the name of the FILEHANDLE at run time.  For more on  formats,
             see the section on formats later on.

             Note that write is NOT the opposite of read.


     Perl operators have the following associativity and precedence:

     nonassoc    print printf exec system sort reverse
                 chmod chown kill unlink utime die return
     left        ,
     right       = += -= *= etc.
     right       ?:
     nonassoc    ..
     left        ||
     left        &&
     left        | ^
     left        &
     nonassoc    == != <=> eq ne cmp
     nonassoc    < > <= >= lt gt le ge
     nonassoc    chdir exit eval reset sleep rand umask
     nonassoc    -r -w -x etc.
     left        << >>
     left        + - .
     left        * / % x
     left        =~ !~
     right       ! ~ and unary minus
     right       **
     nonassoc    ++ --
     left        `('

     As mentioned earlier, if any list operator (print,  etc.)  or  any  unary
     operator  (chdir,  etc.)   is  followed by a left parenthesis as the next
     token on the same line, the operator and arguments within parentheses are
     taken  to  be  of  highest  precedence, just like a normal function call.

              chdir $foo || die;         # (chdir $foo) || die
              chdir($foo) || die;        # (chdir $foo) || die
              chdir ($foo) || die;       # (chdir $foo) || die
              chdir +($foo) || die;      # (chdir $foo) || die

     but, because * is higher precedence than ||:

              chdir $foo * 20;           # chdir ($foo * 20)
              chdir($foo) * 20;          # (chdir $foo) * 20
              chdir ($foo) * 20;         # (chdir $foo) * 20
              chdir +($foo) * 20;        # chdir ($foo * 20)

              rand 10 * 20;              # rand (10 * 20)
              rand(10) * 20;             # (rand 10) * 20
              rand (10) * 20;            # (rand 10) * 20
              rand +(10) * 20;           # rand (10 * 20)

     In the absence of parentheses, the precedence of list operators  such  as
     print, sort or chmod is either very high or very low depending on whether
     you look at the left side of operator or  the  right  side  of  it.   For
     example, in

             @ary = (1, 3, sort 4, 2);
             print @ary;     # prints 1324

     the commas on the right of the sort are evaluated before  the  sort,  but
     the  commas  on  the  left  are  evaluated  after.   In other words, list
     operators tend to gobble up all the arguments that follow them, and  then
     act  like  a  simple  term with regard to the preceding expression.  Note
     that you have to be careful with parens:

             # These evaluate exit before doing the print:
             print($foo, exit); # Obviously not what you want.
             print $foo, exit; # Nor is this.

             # These do the print before evaluating exit:
             (print $foo), exit; # This is what you want.
             print($foo), exit; # Or this.
             print ($foo), exit; # Or even this.

     Also note that

             print ($foo & 255) + 1, "\n";

     probably doesn't do what you expect at first glance.


     A subroutine may be declared as follows:

         sub NAME BLOCK

     Any arguments passed to the routine come in as array @_, that is  ($_[0],
     $_[1],  ...).   The  array  @_  is  a  local  array,  but  its values are
     references to the actual scalar parameters.   The  return  value  of  the
     subroutine  is  the  value  of  the last expression evaluated, and can be
     either an array value or a scalar value.  Alternately, a return statement
     may  be  used  to specify the returned value and exit the subroutine.  To
     create local variables see the local operator.

     A subroutine is called using the do operator or the & operator.


             sub MAX {
                     local($max) = pop(@_);
                     foreach $foo (@_) {
                             $max = $foo if $max < $foo;

             $bestday = &MAX($mon,$tue,$wed,$thu,$fri);


             # get a line, combining continuation lines
             #  that start with whitespace
             sub get_line {
                     $thisline = $lookahead;
                     line: while ($lookahead = <STDIN>) {
                             if ($lookahead =~ /^[ \t]/) {
                                     $thisline .= $lookahead;
                             else {
                                     last line;

             $lookahead = <STDIN>; # get first line
             while ($_ = do get_line()) {

     Use array assignment to a local list to name your formal arguments:

             sub maybeset {
                     local($key, $value) = @_;
                     $foo{$key} = $value unless $foo{$key};

     This also has the effect of turning call-by-reference into call-by-value,
     since the assignment copies the values.

     Subroutines may be called recursively.  If a subroutine is  called  using
     the  &  form,  the argument list is optional.  If omitted, no @_ array is
     set up for the subroutine; the @_ array  at  the  time  of  the  call  is
     visible to subroutine instead.

             do foo(1,2,3);  # pass three arguments
             &foo(1,2,3);    # the same

             do foo();       # pass a null list
             &foo();                 # the same
             &foo;                   # pass no arguments----more efficient

     Passing By Reference

     Sometimes you don't want to pass the value of an array  to  a  subroutine
     but  rather  the name of it, so that the subroutine can modify the global
     copy of it rather than working with a local copy.  In perl you can  refer
     to all the objects of a particular name by  prefixing  the  name  with  a
     star:  *foo.   When evaluated, it produces a scalar value that represents
     all the objects  of  that  name,  including  any  filehandle,  format  or
     subroutine.   When  assigned to within a local() operation, it causes the
     name mentioned to refer to whatever * value was assigned to it.  Example:

             sub doubleary {
                local(*someary) = @_;
                foreach $elem (@someary) {
                     $elem *= 2;
             do doubleary(*foo);
             do doubleary(*bar);

     Assignment to *name is currently recommended only inside a local().   You
     can actually assign to *name anywhere, but the previous referent of *name
     may be stranded forever.  This may or may not bother you.

     Note that scalars are already passed by  reference,  so  you  can  modify
     scalar  arguments without using this mechanism by referring explicitly to
     the $_[nnn] in question.  You can modify all the elements of an array  by
     passing  all the elements as scalars, but you have to use the * mechanism
     to push, pop or change the size  of  an  array.   The  *  mechanism  will
     probably be more efficient in any case.

     Since a *name value contains unprintable binary data, if it is used as an
     argument  in a print, or as a %s argument in a printf or sprintf, it then
     has the value '*name', just so it prints out pretty.

     Even if you don't want to modify an array, this mechanism is  useful  for
     passing  multiple  arrays  in  a  single  LIST,  since  normally the LIST
     mechanism will merge all the array values so that you can't  extract  out
     the individual arrays.

     Regular Expressions

     The patterns used in pattern matching are  regular  expressions  such  as
     those  supplied in the Version 8 regexp routines.  (In fact, the routines
     are derived from Henry Spencer's freely redistributable  reimplementation
     of  the  V8 routines.)  In addition, \w matches an alphanumeric character
     (including ``_'') and \W  a  nonalphanumeric.   Word  boundaries  may  be
     matched  by  \b,  and  non-boundaries  by  \B.  A whitespace character is
     matched by \s, non-whitespace by \S.  A numeric character is  matched  by
     \d,  non-numeric  by  \D.   You  may  use  \w, \s and \d within character
     classes.   Also,  \n,  \r,  \f,   \t   and   \NNN   have   their   normal
     interpretations.  Within character classes \b represents backspace rather
     than  a  word  boundary.   Alternatives  may  be  separated  by  |.   The
     bracketing  construct  ( ... )  may  also be used, in which case \<digit>
     matches the digit'th substring.  (Outside of the pattern,  always  use  $
     instead of \ in front of the digit.  The scope of $<digit>  (and  $`,  $&
     and  $')  extends to the end of the enclosing BLOCK or eval string, or to
     the next  pattern  match  with  subexpressions.   The  \<digit>  notation
     sometimes  works  outside  the  current pattern, but should not be relied
     upon.)  You may have as many parentheses as you wish.  If you  have  more
     than 9 substrings, the variables $10, $11, ... refer to the corresponding
     substring.  Within the pattern, \10, \11, etc. refer back  to  substrings
     if   there   have  been  at  least  that  many  left  parens  before  the
     backreference.  Otherwise (for backward compatibilty) \10 is the same  as
     \010,  a  backspace,  and  \11  the same as \011, a tab.  And so on.  (\1
     through \9 are always backreferences.)

     $+ returns whatever the last  bracket  match  matched.   $&  returns  the
     entire  matched  string.   ($0 used to return the same thing, but not any
     more.)  $` returns everything before  the  matched  string.   $'  returns
     everything after the matched string.  Examples:

             s/^([^ ]*) *([^ ]*)/$2 $1/; # swap first two words

             if (/Time: (..):(..):(..)/) {
                     $hours = $1;
                     $minutes = $2;
                     $seconds = $3;

     By default, the ^ character is only guaranteed to match at the  beginning
     of  the string, the $ character only at the end (or before the newline at
     the end) and perl does certain optimizations with the assumption that the
     string  contains  only  one  line.   The  behavior of ^ and $ on embedded
     newlines will be inconsistent.  You may, however, wish to treat a  string
     as  a  multi-line  buffer,  such  that the ^ will match after any newline
     within the string, and $ will match before any newline.  At the cost of a
     little  more  overhead,  you can do this by setting the variable $* to 1.
     Setting it back to 0 makes perl revert to its old behavior.

     To facilitate multi-line substitutions, the . character never  matches  a
     newline  (even  when  $*  is  0).   In particular, the following leaves a
     newline on the $_ string:

             $_ = <STDIN>;

     If the newline is unwanted, try one of

             chop; s/.*(some_string).*/$1/;
             /(some_string)/ && ($_ = $1);

     Any item of a regular expression may be followed  with  digits  in  curly
     brackets  of the form {n,m}, where n gives the minimum number of times to
     match the item and m gives the maximum.  The form {n}  is  equivalent  to
     {n,n}  and  matches  exactly  n  times.   The form {n,} matches n or more
     times.  (If a curly bracket occurs in any other context, it is treated as
     a  regular  character.)   The  *  modifier  is  equivalent to {0,}, the +
     modifier to {1,} and the ? modifier to {0,1}.  There is no limit  to  the
     size of n or m, but large numbers will chew up more memory.

     You  will  note  that  all  backslashed  metacharacters   in   perl   are
     alphanumeric,  such  as \b, \w, \n.  Unlike some other regular expression
     languages, there are no backslashed symbols that aren't alphanumeric.  So
     anything  that  looks  like  \\,  \(,  \),  \<,  \>,  \{, or \} is always
     interpreted as a literal character, not a metacharacter.  This  makes  it
     simple  to quote a string that you want to use for a pattern but that you
     are afraid might contain  metacharacters.   Simply  quote  all  the  non-
     alphanumeric characters:

             $pattern =~ s/(\W)/\\$1/g;


     Output record formats for use with the write  operator  may  declared  as

         format NAME =

     If name is omitted, format ``STDOUT'' is defined.  FORMLIST consists of a
     sequence of lines, each of which may be of one of three types:

     1.  A comment.

     2.  A ``picture'' line giving the format for one output line.

     3.  An argument line supplying values to plug into a picture line.

     Picture lines are printed exactly as they look, except for certain fields
     that  substitute  values  into  the line.  Each picture field starts with
     either @ or ^.  The @ field (not to be confused with the array marker  @)
     is  the  normal case; ^ fields are used to do rudimentary multi-line text
     block filling.  The length of the field is supplied by  padding  out  the
     field  with multiple <, >, or | characters to specify, respectively, left
     justification, right justification, or centering.  As an  alternate  form
     of  right  justification, you may also use # characters (with an optional
     .) to specify a numeric field.  (Use of ^ instead of @ causes  the  field
     to  be  blanked  if  undefined.)  If any of the values supplied for these
     fields contains a newline, only the text up to the  newline  is  printed.
     The special field @* can be used  for  printing  multi-line  values.   It
     should appear by itself on a line.

     The values are specified on the following line, in the same order as  the
     picture fields.  The values should be separated by commas.

     Picture fields that begin with ^ rather than  @  are  treated  specially.
     The  value  supplied must be a scalar variable name which contains a text
     string.  Perl puts as much text as it can into the field, and then  chops
     off  the  front  of  the  string  so  that  the next time the variable is
     referenced, more of the text can be printed.  Normally you  would  use  a
     sequence  of fields in a vertical stack to print out a block of text.  If
     you like, you can end the final field with ..., which will appear in  the
     output  if  the  text  was  too  long to appear in its entirety.  You can
     change which characters are legal to break on by changing the variable $:
     to a list of the desired characters.

     Since use of ^ fields can produce variable length records if the text  to
     be  formatted is short, you can suppress blank lines by putting the tilde
     (~) character anywhere in the line.  (Normally you should put it  in  the
     front  if  possible,  for visibility.)  The tilde will be translated to a
     space upon output.  If you put a second tilde contiguous  to  the  first,
     the line will be repeated until all the fields on the line are exhausted.
     (If you use a field of the @  variety,  the  expression  you  supply  had
     better not give the same value every time forever!)


     # a report on the /etc/passwd file
     format STDOUT_TOP =
                             Passwd File
     Name                Login    Office   Uid   Gid Home
     format STDOUT =
     @<<<<<<<<<<<<<<<<<< @||||||| @<<<<<<@>>>> @>>>> @<<<<<<<<<<<<<<<<<
     $name,              $login,  $office,$uid,$gid, $home

     # a report from a bug report form
     format STDOUT_TOP =
                             Bug Reports
     @<<<<<<<<<<<<<<<<<<<<<<<     @|||         @>>>>>>>>>>>>>>>>>>>>>>>
     $system,                      $%,         $date
     format STDOUT =
     Subject: @<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<
     Index: @<<<<<<<<<<<<<<<<<<<<<<<<<<<< ^<<<<<<<<<<<<<<<<<<<<<<<<<<<<
            $index,                       $description
     Priority: @<<<<<<<<<< Date: @<<<<<<< ^<<<<<<<<<<<<<<<<<<<<<<<<<<<<
               $priority,        $date,   $description
     From: @<<<<<<<<<<<<<<<<<<<<<<<<<<<<< ^<<<<<<<<<<<<<<<<<<<<<<<<<<<<
           $from,                         $description
     Assigned to: @<<<<<<<<<<<<<<<<<<<<<< ^<<<<<<<<<<<<<<<<<<<<<<<<<<<<
                  $programmer,            $description
     ~                                    ^<<<<<<<<<<<<<<<<<<<<<<<<<<<<
     ~                                    ^<<<<<<<<<<<<<<<<<<<<<<<<<<<<
     ~                                    ^<<<<<<<<<<<<<<<<<<<<<<<<<<<<
     ~                                    ^<<<<<<<<<<<<<<<<<<<<<<<<<<<<
     ~                                    ^<<<<<<<<<<<<<<<<<<<<<<<...

     It is possible to intermix prints with writes on the same output channel,
     but you'll have to handle $- (lines left on the page) yourself.

     If you are printing lots of fields that are  usually  blank,  you  should
     consider  using  the reset operator between records.  Not only is it more
     efficient, but it can  prevent  the  bug  of  adding  another  field  and
     forgetting to zero it.

     Interprocess Communication

     The IPC facilities of perl are built on the  Berkeley  socket  mechanism.
     If  you  don't have sockets, you can ignore this section.  The calls have
     the same names as the corresponding system calls, but the arguments  tend
     to  differ,  for  two reasons.  First, perl file handles work differently
     than C file descriptors.  Second, perl already knows the  length  of  its
     strings,  so  you  don't need to pass that information.  Here is a sample
     client (untested):

             ($them,$port) = @ARGV;
             $port = 2345 unless $port;
             $them = 'localhost' unless $them;

             $SIG{'INT'} = 'dokill';
             sub dokill { kill 9,$child if $child; }

             require 'sys/';

             $sockaddr = 'S n a4 x8';
             chop($hostname = `hostname`);

             ($name, $aliases, $proto) = getprotobyname('tcp');
             ($name, $aliases, $port) = getservbyname($port, 'tcp')
                     unless $port =~ /^\d+$/;
             ($name, $aliases, $type, $len, $thisaddr) =
             ($name, $aliases, $type, $len, $thataddr) = gethostbyname($them);

             $this = pack($sockaddr, &AF_INET, 0, $thisaddr);
             $that = pack($sockaddr, &AF_INET, $port, $thataddr);

             socket(S, &PF_INET, &SOCK_STREAM, $proto) || die "socket: $!";
             bind(S, $this) || die "bind: $!";
             connect(S, $that) || die "connect: $!";

             select(S); $| = 1; select(stdout);

             if ($child = fork) {
                     while (<>) {
                             print S;
                     sleep 3;
                     do dokill();
             else {
                     while (<S>) {

     And here's a server:

             ($port) = @ARGV;
             $port = 2345 unless $port;

             require 'sys/';

             $sockaddr = 'S n a4 x8';

             ($name, $aliases, $proto) = getprotobyname('tcp');
             ($name, $aliases, $port) = getservbyname($port, 'tcp')
                     unless $port =~ /^\d+$/;

             $this = pack($sockaddr, &AF_INET, $port, "\0\0\0\0");

             select(NS); $| = 1; select(stdout);

             socket(S, &PF_INET, &SOCK_STREAM, $proto) || die "socket: $!";
             bind(S, $this) || die "bind: $!";
             listen(S, 5) || die "connect: $!";

             select(S); $| = 1; select(stdout);

             for (;;) {
                     print "Listening again\n";
                     ($addr = accept(NS,S)) || die $!;
                     print "accept ok\n";

                     ($af,$port,$inetaddr) = unpack($sockaddr,$addr);
                     @inetaddr = unpack('C4',$inetaddr);
                     print "$af $port @inetaddr\n";

                     while (<NS>) {
                             print NS;

     Predefined Names

     The following names have special meaning to  perl.   I  could  have  used
     alphabetic  symbols  for  some  of  these,  but I didn't want to take the
     chance that someone would say reset ``a-zA-Z'' and  wipe  them  all  out.
     You'll  just have to suffer along with these silly symbols.  Most of them
     have reasonable mnemonics, or analogues in one of the shells.

     $_      The default input and  pattern-searching  space.   The  following
             pairs are equivalent:

                     while (<>) {... # only equivalent in while!
                     while ($_ = <>) {...

                     $_ =~ /^Subject:/

                     $_ =~ y/a-z/A-Z/


             (Mnemonic: underline is understood in certain operations.)

     $.      The current input line number of the  last  filehandle  that  was
             read.   Readonly.   Remember  that  only an explicit close on the
             filehandle resets the  line  number.   Since  <>  never  does  an
             explicit  close, line numbers increase across ARGV files (but see
             examples under eof).  (Mnemonic: many programs use . to mean  the
             current line number.)

     $/      The input record separator, newline by default.  Works like awk's
             RS  variable, including treating blank lines as delimiters if set
             to the null string.  You may set it to a multicharacter string to
             match  a  multi-character  delimiter.   Note  that  setting it to
             "\n\n" means something slightly different than setting it to  "",
             if  the  file contains consecutive blank lines.  Setting it to ""
             will treat two or more consecutive blank lines as a single  blank
             line.   Setting  it  to  "\n\n" will blindly assume that the next
             input character belongs to the next paragraph,  even  if  it's  a
             newline.   (Mnemonic:  /  is used to delimit line boundaries when
             quoting poetry.)

     $,      The output field separator for the  print  operator.   Ordinarily
             the  print  operator simply prints out the comma separated fields
             you specify.  In order to get behavior more like  awk,  set  this
             variable  as  you would set awk's OFS variable to specify what is
             printed between fields.  (Mnemonic: what is printed when there is
             a , in your print statement.)

     $       This  is  like  $,  except  that  it  applies  to  array   values
             interpolated  into a double-quoted string (or similar interpreted
             string).  Default is a space.  (Mnemonic: obvious, I think.)

     $\      The output record separator for the print  operator.   Ordinarily
             the  print  operator simply prints out the comma separated fields
             you  specify,  with  no  trailing  newline  or  record  separator
             assumed.   In  order  to  get  behavior  more  like awk, set this
             variable as you would set awk's ORS variable to specify  what  is
             printed  at  the end of the print.  (Mnemonic: you set $\ instead
             of adding \n at the end of the print.  Also, it's  just  like  /,
             but it's what you get ``back'' from perl.)

     $#      The output format for printed numbers.  This variable is a  half-
             hearted attempt to emulate awk's OFMT variable.  There are times,
             however, when awk and perl have differing notions of what  is  in
             fact numeric.  Also, the initial value is %.20g rather than %.6g,
             so you need to set $# explicitly to get awk's value.   (Mnemonic:
             # is the number sign.)

     $%      The current page number of the currently selected output channel.
             (Mnemonic: % is page number in nroff.)

     $=      The current  page  length  (printable  lines)  of  the  currently
             selected  output  channel.   Default  is  60.   (Mnemonic:  = has
             horizontal lines.)

     $-      The number of lines left on the page of  the  currently  selected
             output channel.  (Mnemonic: lines_on_page - lines_printed.)

     $~      The name of the current report format for the currently  selected
             output  channel.   Default is name of the filehandle.  (Mnemonic:
             brother to $^.)

     $^      The name of the current  top-of-page  format  for  the  currently
             selected  output channel.  Default is name of the filehandle with
             ``_TOP'' appended.  (Mnemonic: points to top of page.)

     $|      If set to nonzero, forces a flush after every write or  print  on
             the  currently selected output channel.  Default is 0.  Note that
             STDOUT will typically be  line  buffered  if  output  is  to  the
             terminal  and block buffered otherwise.  Setting this variable is
             useful primarily when you are outputting to a pipe, such as  when
             you  are  running  a  perl  script  under rsh and want to see the
             output as it's happening.  (Mnemonic: when you want your pipes to
             be piping hot.)

     $$      The process number of the perl running this  script.   (Mnemonic:
             same as shells.)

     $?      The status returned by the last pipe close, backtick (``) command
             or  system  operator.  Note that this is the status word returned
             by the wait() system call, so the exit value of the subprocess is
             actually  ($?  >>  8).   $? & 255 gives which signal, if any, the
             process died from, and whether there was a core dump.  (Mnemonic:
             similar to sh and ksh.)

     $&      The string matched by the  last  successful  pattern  match  (not
             counting  any  matches  hidden within a BLOCK or eval enclosed by
             the current BLOCK).  (Mnemonic: like & in some editors.)

     $`      The string preceding whatever was matched by the last  successful
             pattern  match (not counting any matches hidden within a BLOCK or
             eval enclosed by the current BLOCK).  (Mnemonic: ` often precedes
             a quoted string.)

     $'      The string following whatever was matched by the last  successful
             pattern  match (not counting any matches hidden within a BLOCK or
             eval enclosed by the current BLOCK).  (Mnemonic: ' often  follows
             a quoted string.)  Example:
                     $_ = 'abcdefghi';
                     print "$`:$&:$'\n"; # prints abc:def:ghi

     $+      The last bracket matched by the last  search  pattern.   This  is
             useful  if  you don't know which of a set of alternative patterns
             matched.  For example:

                 /Version: (.*)|Revision: (.*)/ && ($rev = $+);

             (Mnemonic: be positive and forward looking.)

     $*      Set to 1 to do multiline matching within a string, 0 to tell perl
             that  it  can  assume that strings contain a single line, for the
             purpose  of  optimizing  pattern  matches.   Pattern  matches  on
             strings   containing  multiple  newlines  can  produce  confusing
             results when $* is  0.   Default  is  0.   (Mnemonic:  *  matches
             multiple  things.)   Note  that this variable only influences the
             interpretation of ^ and $.  A literal newline can be searched for
             even when $* == 0.

     $0      Contains the name of the file containing the  perl  script  being
             executed.   Assigning  to  $0 modifies the argument area that the
             ps(1) program sees.  (Mnemonic: same as sh and ksh.)

             Contains the subpattern from the corresponding set of parentheses
             in  the  last  pattern  matched, not counting patterns matched in
             nested blocks that have been  exited  already.   (Mnemonic:  like

     $[      The index of the first element in an  array,  and  of  the  first
             character  in a substring.  Default is 0, but you could set it to
             1  to  make  perl  behave  more  like  awk  (or   Fortran)   when
             subscripting   and  when  evaluating  the  index()  and  substr()
             functions.  (Mnemonic: [ begins subscripts.)

     $]      The string printed out when you say ``perl -v''.  It can be  used
             to  determine  at  the  beginning  of  a  script whether the perl
             interpreter executing  the  script  is  in  the  right  range  of
             versions.   If  used  in a numeric context, returns the version +
             patchlevel / 1000.  Example:

                     # see if getc is available
                     ($version,$patchlevel) =
                             $] =~ /(\d+\.\d+).*\nPatch level: (\d+)/;
                     print STDERR "(No filename completion available.)\n"
                             if $version * 1000 + $patchlevel < 2016;

             or, used numerically,

                     warn "No checksumming!\n" if $] < 3.019;

             (Mnemonic: Is this version of perl in the right bracket?)

     $;      The subscript separator for  multi-dimensional  array  emulation.
             If you refer to an associative array element as

             it really means

                     $foo{join($;, $a, $b, $c)}

             But don't put

                     @foo{$a,$b,$c}  # a slice----note the @

             which means


             Default is "\034", the same as SUBSEP in awk.  Note that if  your
             keys  contain  binary  data there might not be any safe value for
             $;.  (Mnemonic: comma (the syntactic subscript  separator)  is  a
             semi-semicolon.   Yeah,  I  know,  it's  pretty  lame,  but $, is
             already taken for something more important.)

     $!      If used in a numeric context, yields the current value of  errno,
             with  all  the  usual  caveats.   (This  means that you shouldn't
             depend on the value of $! to be  anything  in  particular  unless
             you've gotten a specific error return indicating a system error.)
             If used in a string  context,  yields  the  corresponding  system
             error string.  You can assign to $! in order to set errno if, for
             instance, you want $! to return the string for error  n,  or  you
             want to set the exit value for the die operator.  (Mnemonic: What
             just went bang?)

     $@      The perl syntax error message from the  last  eval  command.   If
             null,  the  last eval parsed and executed correctly (although the
             operations you invoked may have failed in  the  normal  fashion).
             (Mnemonic: Where was the syntax error ``at''?)

     $<      The real uid of this process.  (Mnemonic: it's the uid  you  came
             FROM, if you're running setuid.)

     $>      The effective uid of this process.  Example:

                     $< = $>; # set real uid to the effective uid
                     ($<,$>) = ($>,$<); # swap real and effective uid

             (Mnemonic: it's the uid you went TO, if you're  running  setuid.)
             Note:  $<  and  $>  can  only  be  swapped on machines supporting

     $(      The real gid of this process.  If  you  are  on  a  machine  that
             supports  membership  in  multiple groups simultaneously, gives a
             space separated list of groups you are in.  The first  number  is
             the  one  returned  by  getgid(),  and  the  subsequent  ones  by
             getgroups(), one of which may be the same as  the  first  number.
             (Mnemonic: parentheses are used to GROUP things.  The real gid is
             the group you LEFT, if you're running setgid.)

     $)      The effective gid of this process.  If you are on a machine  that
             supports  membership  in  multiple groups simultaneously, gives a
             space separated list of groups you are in.  The first  number  is
             the  one  returned  by  getegid(),  and  the  subsequent  ones by
             getgroups(), one of which may be the same as  the  first  number.
             (Mnemonic:  parentheses  are used to GROUP things.  The effective
             gid is the group that's RIGHT for you, if you're running setgid.)

             Note: $<, $>, $( and $) can only be set on machines that  support
             the corresponding set[re][ug]id() routine.  $( and $) can only be
             swapped on machines supporting setregid().

     $:      The current set of characters after which a string may be  broken
             to  fill  continuation  fields  (starting  with  ^)  in a format.
             Default is " \n-", to break on whitespace or hyphens.  (Mnemonic:
             a ``colon'' in poetry is a part of a line.)

     $^D     The current value of the debugging flags.  (Mnemonic: value of -D

     $^F     The maximum system file descriptor, ordinarily  2.   System  file
             descriptors   are  passed  to  subprocesses,  while  higher  file
             descriptors are not.  During an open, system file descriptors are
             preserved  even if the open fails.  Ordinary file descriptors are
             closed before the open is attempted.

     $^I     The current value of the inplace-edit extension.   Use  undef  to
             disable inplace editing.  (Mnemonic: value of -i switch.)

     $^L     What formats output to perform a formfeed.  Default is \f.

     $^P     The internal flag that the debugger clears  so  that  it  doesn't
             debug  itself.   You could conceivable disable debugging yourself
             by clearing it.

     $^T     The time at which the script began running, in seconds since  the
             epoch.   The  values returned by the -M , -A and -C filetests are
             based on this value.

     $^W     The current value of the warning switch.  (Mnemonic:  related  to
             the -w switch.)

     $^X     The name that Perl itself was executed as, from argv[0].

     $ARGV   contains the name of the current file when reading from <>.

     @ARGV   The array ARGV contains the command line arguments  intended  for
             the  script.   Note  that  $#ARGV  is  the  generally  number  of
             arguments minus one, since $ARGV[0] is the  first  argument,  NOT
             the command name.  See $0 for the command name.

     @INC    The array INC contains the  list  of  places  to  look  for  perl
             scripts  to  be  evaluated  by  the  ``do  EXPR''  command or the
             ``require'' command.  It initially consists of the  arguments  to
             any  -I  command  line  switches,  followed  by  the default perl
             library, probably ``/usr/local/lib/perl'', followed by ``.'',  to
             represent the current directory.

     %INC    The associative array INC contains entries for each filename that
             has  been  included  via  ``do''  or ``require''.  The key is the
             filename you specified, and the value is the location of the file
             actually  found.   The  ``require''  command  uses  this array to
             determine whether a given file has already been included.

             The associative array  ENV  contains  your  current  environment.
             Setting  a  value  in  ENV  changes  the  environment  for  child

             The associative array SIG is used  to  set  signal  handlers  for
             various signals.  Example:

                     sub handler { # 1st argument is signal name
                             local($sig) = @_;
                             print "Caught a SIG$sig--shutting down\n";

                     $SIG{'INT'} = 'handler';
                     $SIG{'QUIT'} = 'handler';
                     $SIG{'INT'} = 'DEFAULT'; # restore default action
                     $SIG{'QUIT'} = 'IGNORE'; # ignore SIGQUIT

             The SIG array only contains values for the signals  actually  set
             within the perl script.


     Perl provides a mechanism for alternate namespaces  to  protect  packages
     from stomping on each others variables.  By default, a perl script starts
     compiling into the package known as ``main''.   By  use  of  the  package
     declaration,  you  can  switch  namespaces.   The  scope  of  the package
     declaration is from the declaration itself to the end  of  the  enclosing
     block  (the  same  scope as the local() operator).  Typically it would be
     the first declaration in  a  file  to  be  included  by  the  ``require''
     operator.   You  can  switch  into  a  package in more than one place; it
     merely influences which symbol table is used by the compiler for the rest
     of  that  block.   You  can  refer  to variables and filehandles in other
     packages by prefixing the identifier with the package name and  a  single
     quote.  If the package name is null, the ``main'' package as assumed.

     Only identifiers starting with letters are stored in the packages  symbol
     table.  All other symbols are kept in package ``main''.  In addition, the
     identifiers STDIN, STDOUT, STDERR, ARGV, ARGVOUT, ENV, INC  and  SIG  are
     forced  to be in package ``main'', even when used for other purposes than
     their built-in one.  Note also that, if you have a package called  ``m'',
     ``s''  or  ``y'',  the  you can't use the qualified form of an identifier
     since it will be interpreted instead as a pattern match,  a  substitution
     or a translation.

     Eval'ed strings are compiled  in  the  package  in  which  the  eval  was
     compiled  in.  (Assignments to $SIG{}, however, assume the signal handler
     specified is in the main package.  Qualify the signal handler name if you
     wish  to  have  a  signal handler in a package.)  For an example, examine in the perl library.  It initially switches to the  DB  package
     so  that  the debugger doesn't interfere with variables in the script you
     are trying to debug.  At various points, however, it temporarily switches
     back  to  the main package to evaluate various expressions in the context
     of the main package.

     The symbol table for a package happens to be stored  in  the  associative
     array of that name prepended with an underscore.  The value in each entry
     of the associative array is what you are referring to when  you  use  the
     *name  notation.  In fact, the following have the same effect (in package
     main, anyway), though the first is more efficient  because  it  does  the
     symbol table lookups at compile time:

             local(*foo) = *bar;
             local($_main{'foo'}) = $_main{'bar'};

     You can use this to print  out  all  the  variables  in  a  package,  for
     instance.  Here is from the perl library:
             package dumpvar;

             sub main'dumpvar {
                 ($package) = @_;
                 local(*stab) = eval("*_$package");
                 while (($key,$val) = each(%stab)) {
                         local(*entry) = $val;
                         if (defined $entry) {
                             print "\$$key = '$entry'\n";
                         if (defined @entry) {
                             print "\@$key = (\n";
                             foreach $num ($[ .. $#entry) {
                                 print "  $num\t'",$entry[$num],"'\n";
                             print ")\n";
                         if ($key ne "_$package" && defined %entry) {
                             print "\%$key = (\n";
                             foreach $key (sort keys(%entry)) {
                                 print "  $key\t'",$entry{$key},"'\n";
                             print ")\n";

     Note that, even though the subroutine is compiled in package dumpvar, the
     name  of  the  subroutine  is qualified so that its name is inserted into
     package ``main''.


     Each programmer will, of course, have  his  or  her  own  preferences  in
     regards  to  formatting,  but there are some general guidelines that will
     make your programs easier to read.
     1.  Just because you CAN do something a particular way doesn't mean  that
         you SHOULD do it that way.  Perl is designed to give you several ways
         to do anything, so consider  picking  the  most  readable  one.   For

                 open(FOO,$foo) || die "Can't open $foo: $!";

         is better than

                 die "Can't open $foo: $!" unless open(FOO,$foo);

         because the second way hides the main point of  the  statement  in  a
         modifier.  On the other hand

                 print "Starting analysis\n" if $verbose;

         is better than

                 $verbose && print "Starting analysis\n";

         since the main point isn't whether the user typed -v or not.

         Similarly, just because an operator lets you assume default arguments
         doesn't mean that you have to make use of the defaults.  The defaults
         are there for lazy systems programmers writing one-shot programs.  If
         you  want  your  program  to  be  readable,  consider  supplying  the

         Along the same lines, just because you can omit parentheses  in  many
         places doesn't mean that you ought to:

                 return print reverse sort num values array;
                 return print(reverse(sort num (values(%array))));

         When in doubt, parenthesize.  At the very least it will let some poor
         schmuck bounce on the % key in vi.

         Even if you aren't in doubt,  consider  the  mental  welfare  of  the
         person  who has to maintain the code after you, and who will probably
         put parens in the wrong place.

     2.  Don't go through silly contortions to exit a loop at the top  or  the
         bottom, when perl provides the "last" operator so you can exit in the
         middle.  Just outdent it a little to make it more visible:

                 for (;;) {
                 last line if $foo;
                    next line if /^#/;

     3.  Don't be afraid  to  use  loop  labels----they're  there  to  enhance
         readability  as  well  as to allow multi-level loop breaks.  See last

     4.  For portability, when using features that may not be  implemented  on
         every  machine, test the construct in an eval to see if it fails.  If
         you  know  what  version  or  patchlevel  a  particular  feature  was
         implemented, you can test $] to see if it will be there.

     5.  Choose mnemonic identifiers.

     6.  Be consistent.


     If you invoke perl with a -d switch, your script  will  be  run  under  a
     debugging  monitor.   It  will halt before the first executable statement
     and ask you for a command, such as:

     h           Prints out a help message.

     T           Stack trace.

     s           Single step.  Executes until  it  reaches  the  beginning  of
                 another statement.

     n           Next.  Executes over subroutine calls, until it  reaches  the
                 beginning of the next statement.

     f           Finish.   Executes  statements  until  it  has  finished  the
                 current subroutine.

     c           Continue.  Executes until the next breakpoint is reached.

     c line      Continue to the  specified  line.   Inserts  a  one-time-only
                 breakpoint at the specified line.

     <CR>        Repeat last n or s.

     l min+incr  List incr+1 lines starting at min.  If min is omitted, starts
                 where  last  listing  left off.  If incr is omitted, previous
                 value of incr is used.

     l min-max   List lines in the indicated range.

     l line      List just the indicated line.

     l           List next window.

     -           List previous window.

     w line      List window around line.

     l subname   List subroutine.  If it's a long subroutine it just lists the
                 beginning.  Use ``l'' to list more.

     /pattern/   Regular expression search forward for pattern; the final / is

     ?pattern?   Regular expression search backward for pattern; the  final  ?
                 is optional.

     L           List lines that have breakpoints or actions.

     S           Lists the names of all subroutines.

     t           Toggle trace mode on or off.

     b line condition
                 Set a breakpoint.  If line is omitted, sets a  breakpoint  on
                 the  line  that  is  about to be executed.  If a condition is
                 specified, it is evaluated each time the statement is reached
                 and  a  breakpoint  is  taken  only if the condition is true.
                 Breakpoints may only be set on lines that begin an executable

     b subname condition
                 Set breakpoint at first executable line of subroutine.

     d line      Delete  breakpoint.   If  line  is   omitted,   deletes   the
                 breakpoint on the line that is about to be executed.

     D           Delete all breakpoints.

     a line command
                 Set an action for line.  A multi-line command may be  entered
                 by backslashing the newlines.

     A           Delete all line actions.

     < command   Set an action to happen  before  every  debugger  prompt.   A
                 multi-line   command  may  be  entered  by  backslashing  the

     > command   Set an action to happen after the  prompt  when  you've  just
                 given  a command to return to executing the script.  A multi-
                 line command may be entered by backslashing the newlines.

     V package   List all variables in package.  Default is main package.

     ! number    Redo a debugging command.  If number is omitted,  redoes  the
                 previous command.

     ! -number   Redo the command that was that many commands ago.

     H -number   Display last n  commands.   Only  commands  longer  than  one
                 character are listed.  If number is omitted, lists them all.

     q or ^D     Quit.

     command     Execute command as a perl  statement.   A  missing  semicolon
                 will be supplied.

     p expr      Same as ``print DB'OUT  expr''.   The  DB'OUT  filehandle  is
                 opened  to  /dev/tty,  regardless  of  where  STDOUT  may  be
                 redirected to.

     If you want to modify the debugger, copy from the perl  library
     to  your current directory and modify it as necessary.  (You'll also have
     to put -I. on your command line.)   You  can  do  some  customization  by
     setting  up  a  .perldb  file  which  contains  initialization code.  For
     instance, you could make aliases like these:

         $DB'alias{'len'} = 's/^len(.*)/p length($1)/';
         $DB'alias{'stop'} = 's/^stop (at|in)/b/';
         $DB'alias{'.'} =
           's/^\./p "\$DB\'sub(\$DB\'line):\t",\$DB\'line[\$DB\'line]/';

     Setuid Scripts

     Perl is designed to make it  easy  to  write  secure  setuid  and  setgid
     scripts.   Unlike shells, which are based on multiple substitution passes
     on each line of the script, perl  uses  a  more  conventional  evaluation
     scheme  with  fewer hidden ``gotchas''.  Additionally, since the language
     has more built-in functionality, it has to rely less upon  external  (and
     possibly untrustworthy) programs to accomplish its purposes.

     In an unpatched 4.2 or 4.3bsd kernel, setuid  scripts  are  intrinsically
     insecure,  but  this  kernel feature can be disabled.  If it is, perl can
     emulate the setuid and setgid mechanism when  it  notices  the  otherwise
     useless  setuid/gid  bits  on  perl scripts.  If the kernel feature isn't
     disabled, perl will complain loudly that your setuid script is  insecure.
     You'll  need to either disable the kernel setuid script feature, or put a
     C wrapper around the script.

     When perl is executing a setuid script, it takes special  precautions  to
     prevent  you  from falling into any obvious traps.  (In some ways, a perl
     script is more secure than the corresponding  C  program.)   Any  command
     line  argument,  environment variable, or input is marked as ``tainted'',
     and may not be used, directly or indirectly, in any command that  invokes
     a  subshell,  or  in  any  command  that  modifies  files, directories or
     processes.  Any variable that  is  set  within  an  expression  that  has
     previously referenced a tainted value also becomes tainted (even if it is
     logically impossible for the tainted value to  influence  the  variable).
     For example:

             $foo = shift;           # $foo is tainted
             $bar = $foo,'bar'; # $bar is also tainted
             $xxx = <>;              # Tainted
             $path = $ENV{'PATH'}; # Tainted, but see below
             $abc = 'abc';           # Not tainted

             system "echo $foo"; # Insecure
             system "/bin/echo", $foo; # Secure (doesn't use sh)
             system "echo $bar"; # Insecure
             system "echo $abc"; # Insecure until PATH set

             $ENV{'PATH'} = '/bin:/usr/bin';
             $ENV{'IFS'} = '' if $ENV{'IFS'} ne '';

             $path = $ENV{'PATH'}; # Not tainted
             system "echo $abc"; # Is secure now!

             open(FOO,"$foo"); # OK
             open(FOO,">$foo"); # Not OK

             open(FOO,"echo $foo|"); # Not OK, but...
             open(FOO,"-|") || exec 'echo', $foo; # OK

             $zzz = `echo $foo`; # Insecure, zzz tainted

             unlink $abc,$foo; # Insecure
             umask $foo;             # Insecure

             exec "echo $foo"; # Insecure
             exec "echo", $foo; # Secure (doesn't use sh)
             exec "sh", '-c', $foo; # Considered secure, alas

     The taintedness is associated with each scalar value, so some elements of
     an array can be tainted, and others not.

     If you try to do something insecure, you will get a  fatal  error  saying
     something  like  ``Insecure dependency'' or ``Insecure PATH''.  Note that
     you can still write  an  insecure  system  call  or  exec,  but  only  by
     explicitly  doing  something  like  the last example above.  You can also
     bypass the tainting mechanism by referencing subpatterns----perl presumes
     that  if  you  reference a substring using $1, $2, etc, you knew what you
     were doing when you wrote the pattern:

             $ARGV[0] =~ /^-P(\w+)$/;
             $printer = $1;  # Not tainted

     This is fairly secure since \w+ doesn't match shell metacharacters.   Use
     of  .+  would have been insecure, but perl doesn't check for that, so you
     must be careful with your patterns.   This  is  the  ONLY  mechanism  for
     untainting  user  supplied filenames if you want to do file operations on
     them (unless you make $> equal to $<).

     It's also possible to get into trouble with other operations  that  don't
     care  whether  they  use  tainted values.  Make judicious use of the file
     tests in dealing with any user-supplied  filenames.   When  possible,  do
     opens  and  such  after  setting  $> = $<.  Perl doesn't prevent you from
     opening tainted filenames for reading, so be careful what you print  out.
     The  tainting  mechanism  is  intended to prevent stupid mistakes, not to
     remove the need for thought.


     HOME        Used if chdir has no argument.

     LOGDIR      Used if chdir has no argument and HOME is not set.

     PATH        Used in executing subprocesses, and in finding the script  if
                 -S is used.

     PERLLIB     A colon-separated list of directories in which  to  look  for
                 Perl library files before looking in the standard library and
                 the current directory.

     PERLDB      The command used to get the debugger code.  If unset, uses

                         require ''

     Apart from these, perl uses no other  environment  variables,  except  to
     make them available to the script being executed, and to child processes.
     However, scripts running setuid would do well to  execute  the  following
     lines before doing anything else, just to keep people honest:
         $ENV{'PATH'} = '/bin:/usr/bin';    # or whatever you need
         $ENV{'SHELL'} = '/bin/sh' if $ENV{'SHELL'} ne '';
         $ENV{'IFS'} = '' if $ENV{'IFS'} ne '';

     Larry Wall <>
     MS-DOS port by Diomidis Spinellis <>

     /tmp/perl-eXXXXXX temporary file for -e commands.

     a2p     awk to perl translator
     s2p     sed to perl translator

     Compilation errors will tell you the line number of the  error,  with  an
     indication  of the next token or token type that was to be examined.  (In
     the case of a script passed to perl via -e switches, each -e  is  counted
     as one line.)

     Setuid  scripts  have  additional  constraints  that  can  produce  error
     messages  such  as  ``Insecure  dependency''.   See the section on setuid

     Accustomed awk users should take special note of the following:

     *   Semicolons are required after all simple statements in  perl  (except
         at the end of a block).  Newline is not a statement delimiter.

     *   Curly brackets are required on ifs and whiles.

     *   Variables begin with $ or @ in perl.

     *   Arrays index from 0 unless you set $[.  Likewise string positions  in
         substr() and index().

     *   You have to decide whether your array has numeric or string indices.

     *   Associative array values do  not  spring  into  existence  upon  mere

     *   You have to  decide  whether  you  want  to  use  string  or  numeric

     *   Reading an input line does not split it for you.  You get to split it
         yourself   to  an  array.   And  the  split  operator  has  different

     *   The current input line is normally in $_, not $0.  It generally  does
         not  have  the  newline  stripped.   ($0  is  the name of the program

     *   $<digit> does not refer to fields----it refers to substrings  matched
         by the last match pattern.

     *   The print statement does not add field and record  separators  unless
         you set $, and $\.

     *   You must open your files before you print to them.

     *   The range operator is ``..'', not comma.  (The comma  operator  works
         as in C.)

     *   The match operator  is  ``=~'',  not  ``~''.   (``~''  is  the  one's
         complement operator, as in C.)

     *   The exponentiation operator is ``**'', not ``^''.  (``^'' is the  XOR
         operator, as in C.)

     *   The concatenation operator is ``.'', not the null string.  (Using the
         null  string would render ``/pat/ /pat/'' unparsable, since the third
         slash would be interpreted as a division operator----the  tokener  is
         in  fact  slightly  context sensitive for operators like /, ?, and <.
         And in fact, . itself can be the beginning of a number.)

     *   Next, exit and continue work differently.

     *   The following variables work differently

                      Awk                              Perl
                      ARGC                             $#ARGV
                      ARGV[0]                          $0
                      FILENAME                         $ARGV
                      FNR                              $. - something
                      FS                               (whatever you like)
                      NF                               $#Fld, or some such
                      NR                               $.
                      OFMT                             $#
                      OFS                              $,
                      ORS                              $\
                      RLENGTH                          length($&)
                      RS                               $/
                      RSTART                           length($`)
                      SUBSEP                           $;

     *   When in doubt, run the awk construct through  a2p  and  see  what  it
         gives you.

     Cerebral C programmers should take note of the following:

     *   Curly brackets are required on ifs and whiles.

     *   You should use ``elsif'' rather than ``else if''

     *   Break and continue become last and next, respectively.

     *   There's no switch statement.

     *   Variables begin with $ or @ in perl.

     *   Printf does not implement *.

     *   Comments begin with #, not /*.

     *   You can't take the address of anything.

     *   ARGV must be capitalized.

     *   The ``system'' calls link, unlink, rename, etc.  return  nonzero  for
         success, not 0.

     *   Signal handlers deal with signal names, not numbers.

     Seasoned sed programmers should take note of the following:

     *   Backreferences in substitutions use $ rather than \.

     *   The  pattern  matching  metacharacters  (,  ),  and  |  do  not  have
         backslashes in front.

     *   The range operator is .. rather than comma.

     Sharp shell programmers should take note of the following:

     *   The backtick operator does variable interpretation without regard  to
         the presence of single quotes in the command.

     *   The backtick operator does no translation of the return value, unlike

     *   Shells (especially csh) do several levels  of  substitution  on  each
         command line.  Perl does substitution only in certain constructs such
         as double quotes, backticks, angle brackets and search patterns.

     *   Shells interpret scripts a little bit at a time.  Perl  compiles  the
         whole program before executing it.

     *   The arguments are available via @ARGV, not $1, $2, etc.

     *   The environment is not automatically made available as variables.

     The Perl book, Programming Perl , has the following omissions and goofs.

     On page 5, the examples which read

             eval "/usr/bin/perl

     should read

             eval "exec /usr/bin/perl

     On page 195, the equivalent to the System V sum program  only  works  for
     very small files.  To do larger files, use

             undef $/;
             $checksum = unpack("%32C*",<>) % 32767;

     The descriptions of alarm and sleep  refer  to  signal  SIGALARM.   These
     should refer to SIGALRM.

     The -0 switch to set the initial value of $/ was added to Perl after  the
     book went to press.

     The -l switch now does automatic line ending processing.

     The qx// construct is now a synonym for backticks.

     $0 may now be assigned to set the argument displayed by ps (1).

     The new @###.## format was omitted accidentally from the  description  on

     It wasn't known at press time that s///ee caused multiple evaluations  of
     the replacement expression.  This is to be construed as a feature.

     (LIST) x $count now does array replication.

     There is now  no  limit  on  the  number  of  parentheses  in  a  regular

     In double-quote context, more escapes are supported: \e, \a,  \x1b,  \c[,
     \l, \L, \u, \U, \E.  The latter five control up/lower case translation.

     The $/ variable may now be set to a multi-character delimiter.

     There is now a g modifier on ordinary pattern matching that causes it  to
     iterate through a string finding multiple matches.

     All of the $^X variables are new except for $^T.

     The default top-of-form  format  for  FILEHANDLE  is  now  FILEHANDLE_TOP
     rather than top.

     The eval {} and sort {} constructs were added in version 4.018.

     The v and V (little-endian) template options for  pack  and  unpack  were
     added in 4.019.


     Perl is at the mercy of your machine's definitions of various  operations
     such as type casting, atof() and sprintf().

     If your stdio requires an seek or eof  between  reads  and  writes  on  a
     particular  stream,  so  does perl.  (This doesn't apply to sysread() and

     While none of the built-in data types  have  any  arbitrary  size  limits
     (apart  from  memory  size),  there  are still a few arbitrary limits:  a
     given identifier may not be longer than 255 characters, and no  component
     of  your PATH may be longer than 255 if you use -S.  A regular expression
     may not compile to more than 32767 bytes internally.

     Perl actually stands for  Pathologically  Eclectic  Rubbish  Lister,  but
     don't tell anyone I said that.